Node-API | Node.js v25.9.0 Documentation

Node-API | Node.js v25.9.0 Documentation
Skip to content
Node.js
About this documentation
Usage and example
Assertion testing
Asynchronous context tracking
Async hooks
Buffer
C++ addons
C/C++ addons with Node-API
C++ embedder API
Child processes
Cluster
Command-line options
Console
Crypto
Debugger
Deprecated APIs
Diagnostics Channel
DNS
Domain
Environment Variables
Errors
Events
File system
Globals
HTTP
HTTP/2
HTTPS
Inspector
Internationalization
Modules: CommonJS modules
Modules: ECMAScript modules
Modules:
node:module
API
Modules: Packages
Modules: TypeScript
Net
Iterable Streams API
OS
Path
Performance hooks
Permissions
Process
Punycode
Query strings
Readline
REPL
Report
Single executable applications
SQLite
Stream
String decoder
Test runner
Timers
TLS/SSL
Trace events
TTY
UDP/datagram
URL
Utilities
V8
VM
WASI
Web Crypto API
Web Streams API
Worker threads
Zlib
Zlib Iterable Compression
Code repository and issue tracker
Table of contents
Node-API
Writing addons in various programming languages
Implications of ABI stability
Enum values in ABI stability
Building
Build tools
node-gyp
CMake.js
Uploading precompiled binaries
node-pre-gyp
prebuild
prebuildify
Usage
Node-API version matrix
Environment life cycle APIs
napi_set_instance_data
napi_get_instance_data
Basic Node-API data types
napi_status
napi_extended_error_info
napi_env
node_api_basic_env
napi_value
napi_threadsafe_function
napi_threadsafe_function_release_mode
napi_threadsafe_function_call_mode
Node-API memory management types
napi_handle_scope
napi_escapable_handle_scope
napi_ref
napi_type_tag
napi_async_cleanup_hook_handle
Node-API callback types
napi_callback_info
napi_callback
node_api_basic_finalize
napi_finalize
napi_async_execute_callback
napi_async_complete_callback
napi_threadsafe_function_call_js
napi_cleanup_hook
napi_async_cleanup_hook
Error handling
Return values
napi_get_last_error_info
Exceptions
napi_throw
napi_throw_error
napi_throw_type_error
napi_throw_range_error
node_api_throw_syntax_error
napi_is_error
napi_create_error
napi_create_type_error
napi_create_range_error
node_api_create_syntax_error
napi_get_and_clear_last_exception
napi_is_exception_pending
napi_fatal_exception
Fatal errors
napi_fatal_error
Object lifetime management
Making handle lifespan shorter than that of the native method
napi_open_handle_scope
napi_close_handle_scope
napi_open_escapable_handle_scope
napi_close_escapable_handle_scope
napi_escape_handle
References to values with a lifespan longer than that of the native method
napi_create_reference
napi_delete_reference
napi_reference_ref
napi_reference_unref
napi_get_reference_value
Cleanup on exit of the current Node.js environment
napi_add_env_cleanup_hook
napi_remove_env_cleanup_hook
napi_add_async_cleanup_hook
napi_remove_async_cleanup_hook
Finalization on the exit of the Node.js environment
Module registration
Working with JavaScript values
Enum types
napi_key_collection_mode
napi_key_filter
napi_key_conversion
napi_valuetype
napi_typedarray_type
Object creation functions
napi_create_array
napi_create_array_with_length
napi_create_arraybuffer
napi_create_buffer
napi_create_buffer_copy
napi_create_date
napi_create_external
napi_create_external_arraybuffer
napi_create_external_buffer
napi_create_object
node_api_create_object_with_properties
napi_create_symbol
node_api_symbol_for
napi_create_typedarray
node_api_create_buffer_from_arraybuffer
napi_create_dataview
Functions to convert from C types to Node-API
napi_create_int32
napi_create_uint32
napi_create_int64
napi_create_double
napi_create_bigint_int64
napi_create_bigint_uint64
napi_create_bigint_words
napi_create_string_latin1
node_api_create_external_string_latin1
napi_create_string_utf16
node_api_create_external_string_utf16
napi_create_string_utf8
Functions to create optimized property keys
node_api_create_property_key_latin1
node_api_create_property_key_utf16
node_api_create_property_key_utf8
Functions to convert from Node-API to C types
napi_get_array_length
napi_get_arraybuffer_info
napi_get_buffer_info
napi_get_prototype
napi_get_typedarray_info
napi_get_dataview_info
napi_get_date_value
napi_get_value_bool
napi_get_value_double
napi_get_value_bigint_int64
napi_get_value_bigint_uint64
napi_get_value_bigint_words
napi_get_value_external
napi_get_value_int32
napi_get_value_int64
napi_get_value_string_latin1
napi_get_value_string_utf8
napi_get_value_string_utf16
napi_get_value_uint32
Functions to get global instances
napi_get_boolean
napi_get_global
napi_get_null
napi_get_undefined
Working with JavaScript values and abstract operations
napi_coerce_to_bool
napi_coerce_to_number
napi_coerce_to_object
napi_coerce_to_string
napi_typeof
napi_instanceof
napi_is_array
napi_is_arraybuffer
napi_is_buffer
napi_is_date
napi_is_error
napi_is_typedarray
napi_is_dataview
napi_strict_equals
napi_detach_arraybuffer
napi_is_detached_arraybuffer
node_api_is_sharedarraybuffer
node_api_create_sharedarraybuffer
Working with JavaScript properties
Structures
napi_property_attributes
napi_property_descriptor
Functions
napi_get_property_names
napi_get_all_property_names
napi_set_property
napi_get_property
napi_has_property
napi_delete_property
napi_has_own_property
napi_set_named_property
napi_get_named_property
napi_has_named_property
napi_set_element
napi_get_element
napi_has_element
napi_delete_element
napi_define_properties
napi_object_freeze
napi_object_seal
node_api_set_prototype
Working with JavaScript functions
napi_call_function
napi_create_function
napi_get_cb_info
napi_get_new_target
napi_new_instance
Object wrap
napi_define_class
napi_wrap
napi_unwrap
napi_remove_wrap
napi_type_tag_object
napi_check_object_type_tag
napi_add_finalizer
node_api_post_finalizer
Simple asynchronous operations
napi_create_async_work
napi_delete_async_work
napi_queue_async_work
napi_cancel_async_work
Custom asynchronous operations
napi_async_init
napi_async_destroy
napi_make_callback
napi_open_callback_scope
napi_close_callback_scope
Version management
napi_get_node_version
napi_get_version
Memory management
napi_adjust_external_memory
Promises
napi_create_promise
napi_resolve_deferred
napi_reject_deferred
napi_is_promise
Script execution
napi_run_script
libuv event loop
napi_get_uv_event_loop
Asynchronous thread-safe function calls
Calling a thread-safe function
Reference counting of thread-safe functions
Deciding whether to keep the process running
napi_create_threadsafe_function
napi_get_threadsafe_function_context
napi_call_threadsafe_function
napi_acquire_threadsafe_function
napi_release_threadsafe_function
napi_ref_threadsafe_function
napi_unref_threadsafe_function
Miscellaneous utilities
node_api_get_module_file_name
Node-API
Stability: 2
- Stable
Node-API (formerly N-API) is an API for building native Addons. It is
independent from the underlying JavaScript runtime (for example, V8) and is
maintained as part of Node.js itself. This API will be Application Binary
Interface (ABI) stable across versions of Node.js. It is intended to insulate
addons from changes in the underlying JavaScript engine and allow modules
compiled for one major version to run on later major versions of Node.js without
recompilation. The
ABI Stability
guide provides a more in-depth explanation.
Addons are built/packaged with the same approach/tools outlined in the section
titled
C++ Addons
. The only difference is the set of APIs that are used by
the native code. Instead of using the V8 or
Native Abstractions for Node.js
APIs, the functions available in Node-API are used.
APIs exposed by Node-API are generally used to create and manipulate
JavaScript values. Concepts and operations generally map to ideas specified
in the ECMA-262 Language Specification. The APIs have the following
properties:
All Node-API calls return a status code of type
napi_status
. This
status indicates whether the API call succeeded or failed.
The API's return value is passed via an out parameter.
All JavaScript values are abstracted behind an opaque type named
napi_value
In case of an error status code, additional information can be obtained
using
napi_get_last_error_info
. More information can be found in the error
handling section
Error handling
Writing addons in various programming languages
Node-API is a C API that ensures ABI stability across Node.js versions
and different compiler levels. With this stability guarantee, it is possible
to write addons in other programming languages on top of Node-API. Refer
to
language and engine bindings
for more programming languages and engines
support details.
node-addon-api
is the official C++ binding that provides a more efficient way to
write C++ code that calls Node-API. This wrapper is a header-only library that offers an inlinable C++ API.
Binaries built with
node-addon-api
will depend on the symbols of the Node-API
C-based functions exported by Node.js. The following code snippet is an example
of
node-addon-api
Object obj
Object
::
New
env
);
obj
"foo"
String
::
New
env
"bar"
);
The above
node-addon-api
C++ code is equivalent to the following C-based
Node-API code:
napi_status status
napi_value object
string
status
napi_create_object
env
object
);
if
status
!=
napi_ok
napi_throw_error
env
...
);
return
status
napi_create_string_utf8
env
"bar"
NAPI_AUTO_LENGTH
string
);
if
status
!=
napi_ok
napi_throw_error
env
...
);
return
status
napi_set_named_property
env
object
"foo"
string
);
if
status
!=
napi_ok
napi_throw_error
env
...
);
return
The end result is that the addon only uses the exported C APIs. Even though
the addon is written in C++, it still gets the benefits of the ABI stability
provided by the C Node-API.
When using
node-addon-api
instead of the C APIs, start with the API
docs
for
node-addon-api
The
Node-API Resource
offers
an excellent orientation and tips for developers just getting started with
Node-API and
node-addon-api
. Additional media resources can be found on the
Node-API Media
page.
Implications of ABI stability
Although Node-API provides an ABI stability guarantee, other parts of Node.js do
not, and any external libraries used from the addon may not. In particular,
none of the following APIs provide an ABI stability guarantee across major
versions:
the Node.js C++ APIs available via any of
#include

#include

#include

#include

the libuv APIs which are also included with Node.js and available via
#include

the V8 API available via
#include

Thus, for an addon to remain ABI-compatible across Node.js major versions, it
must use Node-API exclusively by restricting itself to using
#include

and by checking, for all external libraries that it uses, that the external
library makes ABI stability guarantees similar to Node-API.
Enum values in ABI stability
All enum data types defined in Node-API should be considered as a fixed size
int32_t
value. Bit flag enum types should be explicitly documented, and they
work with bit operators like bit-OR (
) as a bit value. Unless otherwise
documented, an enum type should be considered to be extensible.
A new enum value will be added at the end of the enum definition. An enum value
will not be removed or renamed.
For an enum type returned from a Node-API function, or provided as an out
parameter of a Node-API function, the value is an integer value and an addon
should handle unknown values. New values are allowed to be introduced without
a version guard. For example, when checking
napi_status
in switch statements,
an addon should include a default branch, as new status codes may be introduced
in newer Node.js versions.
For an enum type used in an in-parameter, the result of passing an unknown
integer value to Node-API functions is undefined unless otherwise documented.
A new value is added with a version guard to indicate the Node-API version in
which it was introduced. For example,
napi_get_all_property_names
can be
extended with new enum value of
napi_key_filter
For an enum type used in both in-parameters and out-parameters, new values are
allowed to be introduced without a version guard.
Building
Unlike modules written in JavaScript, developing and deploying Node.js
native addons using Node-API requires an additional set of tools. Besides the
basic tools required to develop for Node.js, the native addon developer
requires a toolchain that can compile C and C++ code into a binary. In
addition, depending upon how the native addon is deployed, the
user
of
the native addon will also need to have a C/C++ toolchain installed.
For Linux developers, the necessary C/C++ toolchain packages are readily
available.
GCC
is widely used in the Node.js community to build and
test across a variety of platforms. For many developers, the
LLVM
compiler infrastructure is also a good choice.
For Mac developers,
Xcode
offers all the required compiler tools.
However, it is not necessary to install the entire Xcode IDE. The following
command installs the necessary toolchain:
xcode-select
--install
For Windows developers,
Visual Studio
offers all the required compiler
tools. However, it is not necessary to install the entire Visual Studio
IDE. The following command installs the necessary toolchain:
npm
install
--global
windows-build-tools
The sections below describe the additional tools available for developing
and deploying Node.js native addons.
Build tools
Both the tools listed here require that
users
of the native
addon have a C/C++ toolchain installed in order to successfully install
the native addon.
node-gyp
node-gyp
is a build system based on the
gyp-next
fork of
Google's
GYP
tool and comes bundled with npm. GYP, and therefore node-gyp,
requires that Python be installed.
Historically, node-gyp has been the tool of choice for building native
addons. It has widespread adoption and documentation. However, some
developers have run into limitations in node-gyp.
CMake.js
CMake.js
is an alternative build system based on
CMake
CMake.js is a good choice for projects that already use CMake or for
developers affected by limitations in node-gyp.
build_with_cmake
is an
example of a CMake-based native addon project.
Uploading precompiled binaries
The three tools listed here permit native addon developers and maintainers
to create and upload binaries to public or private servers. These tools are
typically integrated with CI/CD build systems like
Travis CI
and
AppVeyor
to build and upload binaries for a variety of platforms and
architectures. These binaries are then available for download by users who
do not need to have a C/C++ toolchain installed.
node-pre-gyp
node-pre-gyp
is a tool based on node-gyp that adds the ability to
upload binaries to a server of the developer's choice. node-pre-gyp has
particularly good support for uploading binaries to Amazon S3.
prebuild
prebuild
is a tool that supports builds using either node-gyp or
CMake.js. Unlike node-pre-gyp which supports a variety of servers, prebuild
uploads binaries only to
GitHub releases
. prebuild is a good choice for
GitHub projects using CMake.js.
prebuildify
prebuildify
is a tool based on node-gyp. The advantage of prebuildify is
that the built binaries are bundled with the native addon when it's
uploaded to npm. The binaries are downloaded from npm and are immediately
available to the module user when the native addon is installed.
Usage
In order to use the Node-API functions, include the file
node_api.h
which
is located in the src directory in the node development tree:
#include

This will opt into the default
NAPI_VERSION
for the given release of Node.js.
In order to ensure compatibility with specific versions of Node-API, the version
can be specified explicitly when including the header:
#define
NAPI_VERSION
#include

This restricts the Node-API surface to just the functionality that was available
in the specified (and earlier) versions.
Some of the Node-API surface is experimental and requires explicit opt-in:
#define
NAPI_EXPERIMENTAL
#include

In this case the entire API surface, including any experimental APIs, will be
available to the module code.
Occasionally, experimental features are introduced that affect already-released
and stable APIs. These features can be disabled by an opt-out:
#define
NAPI_EXPERIMENTAL
#define
NODE_API_EXPERIMENTAL_
FEATURE_NAME
_OPT_OUT
#include

where

is the name of an experimental feature that affects both
experimental and stable APIs.
Node-API version matrix
Up until version 9, Node-API versions were additive and versioned
independently from Node.js. This meant that any version was
an extension to the previous version in that it had all of
the APIs from the previous version with some additions. Each
Node.js version only supported a single Node-API version.
For example v18.15.0 supports only Node-API version 8. ABI stability was
achieved because 8 was a strict superset of all previous versions.
As of version 9, while Node-API versions continue to be versioned
independently, an add-on that ran with Node-API version 9 may need
code updates to run with Node-API version 10. ABI stability
is maintained, however, because Node.js versions that support
Node-API versions higher than 8 will support all versions
between 8 and the highest version they support and will default
to providing the version 8 APIs unless an add-on opts into a
higher Node-API version. This approach provides the flexibility
of better optimizing existing Node-API functions while
maintaining ABI stability. Existing add-ons can continue to run without
recompilation using an earlier version of Node-API. If an add-on
needs functionality from a newer Node-API version, changes to existing
code and recompilation will be needed to use those new functions anyway.
In versions of Node.js that support Node-API version 9 and later, defining
NAPI_VERSION=X
and using the existing add-on initialization macros
will bake in the requested Node-API version that will be used at runtime
into the add-on. If
NAPI_VERSION
is not set it will default to 8.
This table may not be up to date in older streams, the most up to date
information is in the latest API documentation in:
Node-API version matrix
Node-API version
Supported In
10
v22.14.0+, 23.6.0+ and all later versions
v18.17.0+, 20.3.0+, 21.0.0 and all later versions
v12.22.0+, v14.17.0+, v15.12.0+, 16.0.0 and all later versions
v10.23.0+, v12.19.0+, v14.12.0+, 15.0.0 and all later versions
v10.20.0+, v12.17.0+, 14.0.0 and all later versions
v10.17.0+, v12.11.0+, 13.0.0 and all later versions
v10.16.0+, v11.8.0+, 12.0.0 and all later versions
v6.14.2*, 8.11.2+, v9.11.0+*, 10.0.0 and all later versions
v8.10.0+*, v9.3.0+*, 10.0.0 and all later versions
v8.6.0+**, v9.0.0+*, 10.0.0 and all later versions
* Node-API was experimental.
** Node.js 8.0.0 included Node-API as experimental. It was released as
Node-API version 1 but continued to evolve until Node.js 8.6.0. The API is
different in versions prior to Node.js 8.6.0. We recommend Node-API version 3 or
later.
Each API documented for Node-API will have a header named
added in:
, and APIs
which are stable will have the additional header
Node-API version:
APIs are directly usable when using a Node.js version which supports
the Node-API version shown in
Node-API version:
or higher.
When using a Node.js version that does not support the
Node-API version:
listed or if there is no
Node-API version:
listed,
then the API will only be available if
#define NAPI_EXPERIMENTAL
precedes the inclusion of
node_api.h
or
js_native_api.h
. If an API appears not to be available on
a version of Node.js which is later than the one shown in
added in:
then
this is most likely the reason for the apparent absence.
The Node-APIs associated strictly with accessing ECMAScript features from native
code can be found separately in
js_native_api.h
and
js_native_api_types.h
The APIs defined in these headers are included in
node_api.h
and
node_api_types.h
. The headers are structured in this way in order to allow
implementations of Node-API outside of Node.js. For those implementations the
Node.js specific APIs may not be applicable.
The Node.js-specific parts of an addon can be separated from the code that
exposes the actual functionality to the JavaScript environment so that the
latter may be used with multiple implementations of Node-API. In the example
below,
addon.c
and
addon.h
refer only to
js_native_api.h
. This ensures
that
addon.c
can be reused to compile against either the Node.js
implementation of Node-API or any implementation of Node-API outside of Node.js.
addon_node.c
is a separate file that contains the Node.js specific entry point
to the addon and which instantiates the addon by calling into
addon.c
when the
addon is loaded into a Node.js environment.
// addon.h
#ifndef
_ADDON_H_
#define
_ADDON_H_
#include

napi_value
create_addon
napi_env
env
);
#endif
// _ADDON_H_
// addon.c
#include
"addon.h"
#define
NODE_API_CALL
env
call
do
napi_status status
call
);
if
status
!=
napi_ok
const
napi_extended_error_info
error_info
NULL
napi_get_last_error_info
((
env
),
error_info
);
const
char
err_message
error_info
->
error_message
bool
is_pending
napi_is_exception_pending
((
env
),
is_pending
);
/* If an exception is already pending, don't rethrow it */
if
is_pending
const
char
message
err_message
==
NULL
"empty error message"
err_message
napi_throw_error
((
env
),
NULL
message
);
return
NULL
while
static
napi_value
DoSomethingUseful
napi_env
env
napi_callback_info
info
// Do something useful.
return
NULL
napi_value
create_addon
napi_env
env
napi_value result
NODE_API_CALL
env
napi_create_object
env
result
));
napi_value exported_function
NODE_API_CALL
env
napi_create_function
env
"doSomethingUseful"
NAPI_AUTO_LENGTH
DoSomethingUseful
NULL
exported_function
));
NODE_API_CALL
env
napi_set_named_property
env
result
"doSomethingUseful"
exported_function
));
return
result
// addon_node.c
#include

#include
"addon.h"
NAPI_MODULE_INIT
/* napi_env env, napi_value exports */
// This function body is expected to return a `napi_value`.
// The variables `napi_env env` and `napi_value exports` may be used within
// the body, as they are provided by the definition of `NAPI_MODULE_INIT()`.
return
create_addon
env
);
Environment life cycle APIs
Section Agents
of the
ECMAScript Language Specification
defines the concept
of an "Agent" as a self-contained environment in which JavaScript code runs.
Multiple such Agents may be started and terminated either concurrently or in
sequence by the process.
A Node.js environment corresponds to an ECMAScript Agent. In the main process,
an environment is created at startup, and additional environments can be created
on separate threads to serve as
worker threads
. When Node.js is embedded in
another application, the main thread of the application may also construct and
destroy a Node.js environment multiple times during the life cycle of the
application process such that each Node.js environment created by the
application may, in turn, during its life cycle create and destroy additional
environments as worker threads.
From the perspective of a native addon this means that the bindings it provides
may be called multiple times, from multiple contexts, and even concurrently from
multiple threads.
Native addons may need to allocate global state which they use during
their life cycle of an Node.js environment such that the state can be
unique to each instance of the addon.
To this end, Node-API provides a way to associate data such that its life cycle
is tied to the life cycle of a Node.js environment.
napi_set_instance_data
Added in: v12.8.0, v10.20.0
N-API Version:
napi_status
napi_set_instance_data
node_api_basic_env
env
void
data
napi_finalize
finalize_cb
void
finalize_hint
);
[in] env
: The environment that the Node-API call is invoked under.
[in] data
: The data item to make available to bindings of this instance.
[in] finalize_cb
: The function to call when the environment is being torn
down. The function receives
data
so that it might free it.
napi_finalize
provides more details.
[in] finalize_hint
: Optional hint to pass to the finalize callback during
collection.
Returns
napi_ok
if the API succeeded.
This API associates
data
with the currently running Node.js environment.
data
can later be retrieved using
napi_get_instance_data()
. Any existing data
associated with the currently running Node.js environment which was set by means
of a previous call to
napi_set_instance_data()
will be overwritten. If a
finalize_cb
was provided by the previous call, it will not be called.
napi_get_instance_data
Added in: v12.8.0, v10.20.0
N-API Version:
napi_status
napi_get_instance_data
node_api_basic_env
env
void
**
data
);
[in] env
: The environment that the Node-API call is invoked under.
[out] data
: The data item that was previously associated with the currently
running Node.js environment by a call to
napi_set_instance_data()
Returns
napi_ok
if the API succeeded.
This API retrieves data that was previously associated with the currently
running Node.js environment via
napi_set_instance_data()
. If no data is set,
the call will succeed and
data
will be set to
NULL
Basic Node-API data types
Node-API exposes the following fundamental data types as abstractions that are
consumed by the various APIs. These APIs should be treated as opaque,
introspectable only with other Node-API calls.
napi_status
Added in: v8.0.0
N-API Version:
Integral status code indicating the success or failure of a Node-API call.
Currently, the following status codes are supported.
typedef
enum
napi_ok
napi_invalid_arg
napi_object_expected
napi_string_expected
napi_name_expected
napi_function_expected
napi_number_expected
napi_boolean_expected
napi_array_expected
napi_generic_failure
napi_pending_exception
napi_cancelled
napi_escape_called_twice
napi_handle_scope_mismatch
napi_callback_scope_mismatch
napi_queue_full
napi_closing
napi_bigint_expected
napi_date_expected
napi_arraybuffer_expected
napi_detachable_arraybuffer_expected
napi_would_deadlock
/* unused */
napi_no_external_buffers_allowed
napi_cannot_run_js
napi_status
If additional information is required upon an API returning a failed status,
it can be obtained by calling
napi_get_last_error_info
napi_extended_error_info
Added in: v8.0.0
N-API Version:
typedef
struct
const
char
error_message
void
engine_reserved
uint32_t
engine_error_code
napi_status error_code
napi_extended_error_info
error_message
: UTF8-encoded string containing a VM-neutral description of
the error.
engine_reserved
: Reserved for VM-specific error details. This is currently
not implemented for any VM.
engine_error_code
: VM-specific error code. This is currently
not implemented for any VM.
error_code
: The Node-API status code that originated with the last error.
See the
Error handling
section for additional information.
napi_env
napi_env
is used to represent a context that the underlying Node-API
implementation can use to persist VM-specific state. This structure is passed
to native functions when they're invoked, and it must be passed back when
making Node-API calls. Specifically, the same
napi_env
that was passed in when
the initial native function was called must be passed to any subsequent
nested Node-API calls. Caching the
napi_env
for the purpose of general reuse,
and passing the
napi_env
between instances of the same addon running on
different
Worker
threads is not allowed. The
napi_env
becomes invalid
when an instance of a native addon is unloaded. Notification of this event is
delivered through the callbacks given to
napi_add_env_cleanup_hook
and
napi_set_instance_data
node_api_basic_env
Stability: 1 - Experimental
This variant of
napi_env
is passed to synchronous finalizers
node_api_basic_finalize
). There is a subset of Node-APIs which accept
a parameter of type
node_api_basic_env
as their first argument. These APIs do
not access the state of the JavaScript engine and are thus safe to call from
synchronous finalizers. Passing a parameter of type
napi_env
to these APIs is
allowed, however, passing a parameter of type
node_api_basic_env
to APIs that
access the JavaScript engine state is not allowed. Attempting to do so without
a cast will produce a compiler warning or an error when add-ons are compiled
with flags which cause them to emit warnings and/or errors when incorrect
pointer types are passed into a function. Calling such APIs from a synchronous
finalizer will ultimately result in the termination of the application.
napi_value
This is an opaque pointer that is used to represent a JavaScript value.
napi_threadsafe_function
Added in: v10.6.0
N-API Version:
This is an opaque pointer that represents a JavaScript function which can be
called asynchronously from multiple threads via
napi_call_threadsafe_function()
napi_threadsafe_function_release_mode
Added in: v10.6.0
N-API Version:
A value to be given to
napi_release_threadsafe_function()
to indicate whether
the thread-safe function is to be closed immediately (
napi_tsfn_abort
) or
merely released (
napi_tsfn_release
) and thus available for subsequent use via
napi_acquire_threadsafe_function()
and
napi_call_threadsafe_function()
typedef
enum
napi_tsfn_release
napi_tsfn_abort
napi_threadsafe_function_release_mode
napi_threadsafe_function_call_mode
Added in: v10.6.0
N-API Version:
A value to be given to
napi_call_threadsafe_function()
to indicate whether
the call should block whenever the queue associated with the thread-safe
function is full.
typedef
enum
napi_tsfn_nonblocking
napi_tsfn_blocking
napi_threadsafe_function_call_mode
Node-API memory management types
napi_handle_scope
This is an abstraction used to control and modify the lifetime of objects
created within a particular scope. In general, Node-API values are created
within the context of a handle scope. When a native method is called from
JavaScript, a default handle scope will exist. If the user does not explicitly
create a new handle scope, Node-API values will be created in the default handle
scope. For any invocations of code outside the execution of a native method
(for instance, during a libuv callback invocation), the module is required to
create a scope before invoking any functions that can result in the creation
of JavaScript values.
Handle scopes are created using
napi_open_handle_scope
and are destroyed
using
napi_close_handle_scope
. Closing the scope can indicate to the GC
that all
napi_value
s created during the lifetime of the handle scope are no
longer referenced from the current stack frame.
For more details, review the
Object lifetime management
napi_escapable_handle_scope
Added in: v8.0.0
N-API Version:
Escapable handle scopes are a special type of handle scope to return values
created within a particular handle scope to a parent scope.
napi_ref
Added in: v8.0.0
N-API Version:
This is the abstraction to use to reference a
napi_value
. This allows for
users to manage the lifetimes of JavaScript values, including defining their
minimum lifetimes explicitly.
For more details, review the
Object lifetime management
napi_type_tag
Added in: v14.8.0, v12.19.0
N-API Version:
A 128-bit value stored as two unsigned 64-bit integers. It serves as a UUID
with which JavaScript objects or
externals
can be "tagged" in order to
ensure that they are of a certain type. This is a stronger check than
napi_instanceof
, because the latter can report a false positive if the
object's prototype has been manipulated. Type-tagging is most useful in
conjunction with
napi_wrap
because it ensures that the pointer retrieved
from a wrapped object can be safely cast to the native type corresponding to the
type tag that had been previously applied to the JavaScript object.
typedef
struct
uint64_t
lower
uint64_t
upper
napi_type_tag
napi_async_cleanup_hook_handle
Added in: v14.10.0, v12.19.0
An opaque value returned by
napi_add_async_cleanup_hook
. It must be passed
to
napi_remove_async_cleanup_hook
when the chain of asynchronous cleanup
events completes.
Node-API callback types
napi_callback_info
Added in: v8.0.0
N-API Version:
Opaque datatype that is passed to a callback function. It can be used for
getting additional information about the context in which the callback was
invoked.
napi_callback
Added in: v8.0.0
N-API Version:
Function pointer type for user-provided native functions which are to be
exposed to JavaScript via Node-API. Callback functions should satisfy the
following signature:
typedef
napi_value
napi_callback
)(
napi_env
napi_callback_info
);
Unless for reasons discussed in
Object Lifetime Management
, creating a
handle and/or callback scope inside a
napi_callback
is not necessary.
node_api_basic_finalize
Added in: v21.6.0, v20.12.0, v18.20.0
Stability: 1 - Experimental
Function pointer type for add-on provided functions that allow the user to be
notified when externally-owned data is ready to be cleaned up because the
object it was associated with has been garbage-collected. The user must provide
a function satisfying the following signature which would get called upon the
object's collection. Currently,
node_api_basic_finalize
can be used for
finding out when objects that have external data are collected.
typedef
void
node_api_basic_finalize
)(
node_api_basic_env env
void
finalize_data
void
finalize_hint
);
Unless for reasons discussed in
Object Lifetime Management
, creating a
handle and/or callback scope inside the function body is not necessary.
Since these functions may be called while the JavaScript engine is in a state
where it cannot execute JavaScript code, only Node-APIs which accept a
node_api_basic_env
as their first parameter may be called.
node_api_post_finalizer
can be used to schedule Node-API calls that
require access to the JavaScript engine's state to run after the current
garbage collection cycle has completed.
In the case of
node_api_create_external_string_latin1
and
node_api_create_external_string_utf16
the
env
parameter may be null,
because external strings can be collected during the latter part of environment
shutdown.
Change History:
experimental (
NAPI_EXPERIMENTAL
):
Only Node-API calls that accept a
node_api_basic_env
as their first
parameter may be called, otherwise the application will be terminated with an
appropriate error message. This feature can be turned off by defining
NODE_API_EXPERIMENTAL_BASIC_ENV_OPT_OUT
napi_finalize
Added in: v8.0.0
N-API Version:
Function pointer type for add-on provided function that allow the user to
schedule a group of calls to Node-APIs in response to a garbage collection
event, after the garbage collection cycle has completed. These function
pointers can be used with
node_api_post_finalizer
typedef
void
napi_finalize
)(
napi_env env
void
finalize_data
void
finalize_hint
);
Change History:
experimental (
NAPI_EXPERIMENTAL
is defined):
A function of this type may no longer be used as a finalizer, except with
node_api_post_finalizer
node_api_basic_finalize
must be used
instead. This feature can be turned off by defining
NODE_API_EXPERIMENTAL_BASIC_ENV_OPT_OUT
napi_async_execute_callback
Added in: v8.0.0
N-API Version:
Function pointer used with functions that support asynchronous
operations. Callback functions must satisfy the following signature:
typedef
void
napi_async_execute_callback
)(
napi_env env
void
data
);
Implementations of this function must avoid making Node-API calls that execute
JavaScript or interact with JavaScript objects. Node-API calls should be in the
napi_async_complete_callback
instead. Do not use the
napi_env
parameter as
it will likely result in execution of JavaScript.
napi_async_complete_callback
Added in: v8.0.0
N-API Version:
Function pointer used with functions that support asynchronous
operations. Callback functions must satisfy the following signature:
typedef
void
napi_async_complete_callback
)(
napi_env env
napi_status status
void
data
);
Unless for reasons discussed in
Object Lifetime Management
, creating a
handle and/or callback scope inside the function body is not necessary.
napi_threadsafe_function_call_js
Added in: v10.6.0
N-API Version:
Function pointer used with asynchronous thread-safe function calls. The callback
will be called on the main thread. Its purpose is to use a data item arriving
via the queue from one of the secondary threads to construct the parameters
necessary for a call into JavaScript, usually via
napi_call_function
, and then
make the call into JavaScript.
The data arriving from the secondary thread via the queue is given in the
data
parameter and the JavaScript function to call is given in the
js_callback
parameter.
Node-API sets up the environment prior to calling this callback, so it is
sufficient to call the JavaScript function via
napi_call_function
rather than
via
napi_make_callback
Callback functions must satisfy the following signature:
typedef
void
napi_threadsafe_function_call_js
)(
napi_env env
napi_value js_callback
void
context
void
data
);
[in] env
: The environment to use for API calls, or
NULL
if the thread-safe
function is being torn down and
data
may need to be freed.
[in] js_callback
: The JavaScript function to call, or
NULL
if the
thread-safe function is being torn down and
data
may need to be freed. It
may also be
NULL
if the thread-safe function was created without
js_callback
[in] context
: The optional data with which the thread-safe function was
created.
[in] data
: Data created by the secondary thread. It is the responsibility of
the callback to convert this native data to JavaScript values (with Node-API
functions) that can be passed as parameters when
js_callback
is invoked.
This pointer is managed entirely by the threads and this callback. Thus this
callback should free the data.
Unless for reasons discussed in
Object Lifetime Management
, creating a
handle and/or callback scope inside the function body is not necessary.
napi_cleanup_hook
Added in: v19.2.0, v18.13.0
N-API Version:
Function pointer used with
napi_add_env_cleanup_hook
. It will be called
when the environment is being torn down.
Callback functions must satisfy the following signature:
typedef
void
napi_cleanup_hook
)(
void
data
);
[in] data
: The data that was passed to
napi_add_env_cleanup_hook
napi_async_cleanup_hook
Added in: v14.10.0, v12.19.0
Function pointer used with
napi_add_async_cleanup_hook
. It will be called
when the environment is being torn down.
Callback functions must satisfy the following signature:
typedef
void
napi_async_cleanup_hook
)(
napi_async_cleanup_hook_handle handle
void
data
);
[in] handle
: The handle that must be passed to
napi_remove_async_cleanup_hook
after completion of the asynchronous
cleanup.
[in] data
: The data that was passed to
napi_add_async_cleanup_hook
The body of the function should initiate the asynchronous cleanup actions at the
end of which
handle
must be passed in a call to
napi_remove_async_cleanup_hook
Error handling
Node-API uses both return values and JavaScript exceptions for error handling.
The following sections explain the approach for each case.
Return values
Added in: v8.0.0
N-API Version:
All of the Node-API functions share the same error handling pattern. The
return type of all API functions is
napi_status
The return value will be
napi_ok
if the request was successful and
no uncaught JavaScript exception was thrown. If an error occurred AND
an exception was thrown, the
napi_status
value for the error
will be returned. If an exception was thrown, and no error occurred,
napi_pending_exception
will be returned.
In cases where a return value other than
napi_ok
or
napi_pending_exception
is returned,
napi_is_exception_pending
must be called to check if an exception is pending.
See the section on exceptions for more details.
The full set of possible
napi_status
values is defined
in
napi_api_types.h
The
napi_status
return value provides a VM-independent representation of
the error which occurred. In some cases it is useful to be able to get
more detailed information, including a string representing the error as well as
VM (engine)-specific information.
In order to retrieve this information
napi_get_last_error_info
is provided which returns a
napi_extended_error_info
structure.
The format of the
napi_extended_error_info
structure is as follows:
typedef
struct
napi_extended_error_info
const
char
error_message
void
engine_reserved
uint32_t
engine_error_code
napi_status error_code
};
error_message
: Textual representation of the error that occurred.
engine_reserved
: Opaque handle reserved for engine use only.
engine_error_code
: VM specific error code.
error_code
: Node-API status code for the last error.
napi_get_last_error_info
returns the information for the last
Node-API call that was made.
Do not rely on the content or format of any of the extended information as it
is not subject to SemVer and may change at any time. It is intended only for
logging purposes.
napi_get_last_error_info
Added in: v8.0.0
N-API Version:
napi_status
napi_get_last_error_info
node_api_basic_env
env
const
napi_extended_error_info
**
result
);
[in] env
: The environment that the API is invoked under.
[out] result
: The
napi_extended_error_info
structure with more
information about the error.
Returns
napi_ok
if the API succeeded.
This API retrieves a
napi_extended_error_info
structure with information
about the last error that occurred.
The content of the
napi_extended_error_info
returned is only valid up until
a Node-API function is called on the same
env
. This includes a call to
napi_is_exception_pending
so it may often be necessary to make a copy
of the information so that it can be used later. The pointer returned
in
error_message
points to a statically-defined string so it is safe to use
that pointer if you have copied it out of the
error_message
field (which will
be overwritten) before another Node-API function was called.
Do not rely on the content or format of any of the extended information as it
is not subject to SemVer and may change at any time. It is intended only for
logging purposes.
This API can be called even if there is a pending JavaScript exception.
Exceptions
Any Node-API function call may result in a pending JavaScript exception. This is
the case for any of the API functions, even those that may not cause the
execution of JavaScript.
If the
napi_status
returned by a function is
napi_ok
then no
exception is pending and no additional action is required. If the
napi_status
returned is anything other than
napi_ok
or
napi_pending_exception
, in order to try to recover and continue
instead of simply returning immediately,
napi_is_exception_pending
must be called in order to determine if an exception is pending or not.
In many cases when a Node-API function is called and an exception is
already pending, the function will return immediately with a
napi_status
of
napi_pending_exception
. However, this is not the case
for all functions. Node-API allows a subset of the functions to be
called to allow for some minimal cleanup before returning to JavaScript.
In that case,
napi_status
will reflect the status for the function. It
will not reflect previous pending exceptions. To avoid confusion, check
the error status after every function call.
When an exception is pending one of two approaches can be employed.
The first approach is to do any appropriate cleanup and then return so that
execution will return to JavaScript. As part of the transition back to
JavaScript, the exception will be thrown at the point in the JavaScript
code where the native method was invoked. The behavior of most Node-API calls
is unspecified while an exception is pending, and many will simply return
napi_pending_exception
, so do as little as possible and then return to
JavaScript where the exception can be handled.
The second approach is to try to handle the exception. There will be cases
where the native code can catch the exception, take the appropriate action,
and then continue. This is only recommended in specific cases
where it is known that the exception can be safely handled. In these
cases
napi_get_and_clear_last_exception
can be used to get and
clear the exception. On success, result will contain the handle to
the last JavaScript
Object
thrown. If it is determined, after
retrieving the exception, the exception cannot be handled after all
it can be re-thrown it with
napi_throw
where error is the
JavaScript value to be thrown.
The following utility functions are also available in case native code
needs to throw an exception or determine if a
napi_value
is an instance
of a JavaScript
Error
object:
napi_throw_error
napi_throw_type_error
napi_throw_range_error
node_api_throw_syntax_error
and
napi_is_error
The following utility functions are also available in case native
code needs to create an
Error
object:
napi_create_error
napi_create_type_error
napi_create_range_error
and
node_api_create_syntax_error
where result is the
napi_value
that refers to the newly created
JavaScript
Error
object.
The Node.js project is adding error codes to all of the errors
generated internally. The goal is for applications to use these
error codes for all error checking. The associated error messages
will remain, but will only be meant to be used for logging and
display with the expectation that the message can change without
SemVer applying. In order to support this model with Node-API, both
in internal functionality and for module specific functionality
(as its good practice), the
throw_
and
create_
functions
take an optional code parameter which is the string for the code
to be added to the error object. If the optional parameter is
NULL
then no code will be associated with the error. If a code is provided,
the name associated with the error is also updated to be:
originalName [code]
where
originalName
is the original name associated with the error
and
code
is the code that was provided. For example, if the code
is
'ERR_ERROR_1'
and a
TypeError
is being created the name will be:
TypeError [ERR_ERROR_1]
napi_throw
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_throw
napi_env
env
napi_value
error
);
[in] env
: The environment that the API is invoked under.
[in] error
: The JavaScript value to be thrown.
Returns
napi_ok
if the API succeeded.
This API throws the JavaScript value provided.
napi_throw_error
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_throw_error
napi_env
env
const
char
code
const
char
msg
);
[in] env
: The environment that the API is invoked under.
[in] code
: Optional error code to be set on the error.
[in] msg
: C string representing the text to be associated with the error.
Returns
napi_ok
if the API succeeded.
This API throws a JavaScript
Error
with the text provided.
napi_throw_type_error
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_throw_type_error
napi_env
env
const
char
code
const
char
msg
);
[in] env
: The environment that the API is invoked under.
[in] code
: Optional error code to be set on the error.
[in] msg
: C string representing the text to be associated with the error.
Returns
napi_ok
if the API succeeded.
This API throws a JavaScript
TypeError
with the text provided.
napi_throw_range_error
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_throw_range_error
napi_env
env
const
char
code
const
char
msg
);
[in] env
: The environment that the API is invoked under.
[in] code
: Optional error code to be set on the error.
[in] msg
: C string representing the text to be associated with the error.
Returns
napi_ok
if the API succeeded.
This API throws a JavaScript
RangeError
with the text provided.
node_api_throw_syntax_error
Added in: v17.2.0, v16.14.0
N-API Version:
NAPI_EXTERN napi_status
node_api_throw_syntax_error
napi_env
env
const
char
code
const
char
msg
);
[in] env
: The environment that the API is invoked under.
[in] code
: Optional error code to be set on the error.
[in] msg
: C string representing the text to be associated with the error.
Returns
napi_ok
if the API succeeded.
This API throws a JavaScript
SyntaxError
with the text provided.
napi_is_error
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_is_error
napi_env
env
napi_value
value
bool
result
);
[in] env
: The environment that the API is invoked under.
[in] value
: The
napi_value
to be checked.
[out] result
: Boolean value that is set to true if
napi_value
represents
an error, false otherwise.
Returns
napi_ok
if the API succeeded.
This API queries a
napi_value
to check if it represents an error object.
napi_create_error
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_create_error
napi_env
env
napi_value
code
napi_value
msg
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] code
: Optional
napi_value
with the string for the error code to be
associated with the error.
[in] msg
napi_value
that references a JavaScript
string
to be used as
the message for the
Error
[out] result
napi_value
representing the error created.
Returns
napi_ok
if the API succeeded.
This API returns a JavaScript
Error
with the text provided.
napi_create_type_error
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_create_type_error
napi_env
env
napi_value
code
napi_value
msg
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] code
: Optional
napi_value
with the string for the error code to be
associated with the error.
[in] msg
napi_value
that references a JavaScript
string
to be used as
the message for the
Error
[out] result
napi_value
representing the error created.
Returns
napi_ok
if the API succeeded.
This API returns a JavaScript
TypeError
with the text provided.
napi_create_range_error
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_create_range_error
napi_env
env
napi_value
code
napi_value
msg
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] code
: Optional
napi_value
with the string for the error code to be
associated with the error.
[in] msg
napi_value
that references a JavaScript
string
to be used as
the message for the
Error
[out] result
napi_value
representing the error created.
Returns
napi_ok
if the API succeeded.
This API returns a JavaScript
RangeError
with the text provided.
node_api_create_syntax_error
Added in: v17.2.0, v16.14.0
N-API Version:
NAPI_EXTERN napi_status
node_api_create_syntax_error
napi_env
env
napi_value
code
napi_value
msg
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] code
: Optional
napi_value
with the string for the error code to be
associated with the error.
[in] msg
napi_value
that references a JavaScript
string
to be used as
the message for the
Error
[out] result
napi_value
representing the error created.
Returns
napi_ok
if the API succeeded.
This API returns a JavaScript
SyntaxError
with the text provided.
napi_get_and_clear_last_exception
Added in: v8.0.0
N-API Version:
napi_status
napi_get_and_clear_last_exception
napi_env
env
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[out] result
: The exception if one is pending,
NULL
otherwise.
Returns
napi_ok
if the API succeeded.
This API can be called even if there is a pending JavaScript exception.
napi_is_exception_pending
Added in: v8.0.0
N-API Version:
napi_status
napi_is_exception_pending
napi_env
env
bool
result
);
[in] env
: The environment that the API is invoked under.
[out] result
: Boolean value that is set to true if an exception is pending.
Returns
napi_ok
if the API succeeded.
This API can be called even if there is a pending JavaScript exception.
napi_fatal_exception
Added in: v9.10.0
N-API Version:
napi_status
napi_fatal_exception
napi_env
env
napi_value
err
);
[in] env
: The environment that the API is invoked under.
[in] err
: The error that is passed to
'uncaughtException'
Trigger an
'uncaughtException'
in JavaScript. Useful if an async
callback throws an exception with no way to recover.
Fatal errors
In the event of an unrecoverable error in a native addon, a fatal error can be
thrown to immediately terminate the process.
napi_fatal_error
Added in: v8.2.0
N-API Version:
NAPI_NO_RETURN
void
napi_fatal_error
const
char
location
size_t
location_len
const
char
message
size_t
message_len
);
[in] location
: Optional location at which the error occurred.
[in] location_len
: The length of the location in bytes, or
NAPI_AUTO_LENGTH
if it is null-terminated.
[in] message
: The message associated with the error.
[in] message_len
: The length of the message in bytes, or
NAPI_AUTO_LENGTH
if it is null-terminated.
The function call does not return, the process will be terminated.
This API can be called even if there is a pending JavaScript exception.
Object lifetime management
As Node-API calls are made, handles to objects in the heap for the underlying
VM may be returned as
napi_values
. These handles must hold the
objects 'live' until they are no longer required by the native code,
otherwise the objects could be collected before the native code was
finished using them.
As object handles are returned they are associated with a
'scope'. The lifespan for the default scope is tied to the lifespan
of the native method call. The result is that, by default, handles
remain valid and the objects associated with these handles will be
held live for the lifespan of the native method call.
In many cases, however, it is necessary that the handles remain valid for
either a shorter or longer lifespan than that of the native method.
The sections which follow describe the Node-API functions that can be used
to change the handle lifespan from the default.
Making handle lifespan shorter than that of the native method
It is often necessary to make the lifespan of handles shorter than
the lifespan of a native method. For example, consider a native method
that has a loop which iterates through the elements in a large array:
for
int
1000000
++
napi_value result
napi_status status
napi_get_element
env
object
result
);
if
status
!=
napi_ok
break
// do something with element
This would result in a large number of handles being created, consuming
substantial resources. In addition, even though the native code could only
use the most recent handle, all of the associated objects would also be
kept alive since they all share the same scope.
To handle this case, Node-API provides the ability to establish a new 'scope' to
which newly created handles will be associated. Once those handles
are no longer required, the scope can be 'closed' and any handles associated
with the scope are invalidated. The methods available to open/close scopes are
napi_open_handle_scope
and
napi_close_handle_scope
Node-API only supports a single nested hierarchy of scopes. There is only one
active scope at any time, and all new handles will be associated with that
scope while it is active. Scopes must be closed in the reverse order from
which they are opened. In addition, all scopes created within a native method
must be closed before returning from that method.
Taking the earlier example, adding calls to
napi_open_handle_scope
and
napi_close_handle_scope
would ensure that at most a single handle
is valid throughout the execution of the loop:
for
int
1000000
++
napi_handle_scope scope
napi_status status
napi_open_handle_scope
env
scope
);
if
status
!=
napi_ok
break
napi_value result
status
napi_get_element
env
object
result
);
if
status
!=
napi_ok
break
// do something with element
status
napi_close_handle_scope
env
scope
);
if
status
!=
napi_ok
break
When nesting scopes, there are cases where a handle from an
inner scope needs to live beyond the lifespan of that scope. Node-API supports
an 'escapable scope' in order to support this case. An escapable scope
allows one handle to be 'promoted' so that it 'escapes' the
current scope and the lifespan of the handle changes from the current
scope to that of the outer scope.
The methods available to open/close escapable scopes are
napi_open_escapable_handle_scope
and
napi_close_escapable_handle_scope
The request to promote a handle is made through
napi_escape_handle
which
can only be called once.
napi_open_handle_scope
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_open_handle_scope
napi_env
env
napi_handle_scope
result
);
[in] env
: The environment that the API is invoked under.
[out] result
napi_value
representing the new scope.
Returns
napi_ok
if the API succeeded.
This API opens a new scope.
napi_close_handle_scope
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_close_handle_scope
napi_env
env
napi_handle_scope
scope
);
[in] env
: The environment that the API is invoked under.
[in] scope
napi_value
representing the scope to be closed.
Returns
napi_ok
if the API succeeded.
This API closes the scope passed in. Scopes must be closed in the
reverse order from which they were created.
This API can be called even if there is a pending JavaScript exception.
napi_open_escapable_handle_scope
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_open_escapable_handle_scope
napi_env
env
napi_handle_scope
result
);
[in] env
: The environment that the API is invoked under.
[out] result
napi_value
representing the new scope.
Returns
napi_ok
if the API succeeded.
This API opens a new scope from which one object can be promoted
to the outer scope.
napi_close_escapable_handle_scope
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_close_escapable_handle_scope
napi_env
env
napi_handle_scope
scope
);
[in] env
: The environment that the API is invoked under.
[in] scope
napi_value
representing the scope to be closed.
Returns
napi_ok
if the API succeeded.
This API closes the scope passed in. Scopes must be closed in the
reverse order from which they were created.
This API can be called even if there is a pending JavaScript exception.
napi_escape_handle
Added in: v8.0.0
N-API Version:
napi_status
napi_escape_handle
napi_env
env
napi_escapable_handle_scope
scope
napi_value
escapee
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] scope
napi_value
representing the current scope.
[in] escapee
napi_value
representing the JavaScript
Object
to be
escaped.
[out] result
napi_value
representing the handle to the escaped
Object
in the outer scope.
Returns
napi_ok
if the API succeeded.
This API promotes the handle to the JavaScript object so that it is valid
for the lifetime of the outer scope. It can only be called once per scope.
If it is called more than once an error will be returned.
This API can be called even if there is a pending JavaScript exception.
References to values with a lifespan longer than that of the native method
In some cases, an addon will need to be able to create and reference values
with a lifespan longer than that of a single native method invocation. For
example, to create a constructor and later use that constructor
in a request to create instances, it must be possible to reference
the constructor object across many different instance creation requests. This
would not be possible with a normal handle returned as a
napi_value
as
described in the earlier section. The lifespan of a normal handle is
managed by scopes and all scopes must be closed before the end of a native
method.
Node-API provides methods for creating persistent references to values.
Currently Node-API only allows references to be created for a
limited set of value types, including object, external, function, and symbol.
Each reference has an associated count with a value of 0 or higher,
which determines whether the reference will keep the corresponding value alive.
References with a count of 0 do not prevent values from being collected.
Values of object (object, function, external) and symbol types are becoming
'weak' references and can still be accessed while they are not collected.
Any count greater than 0 will prevent the values from being collected.
Symbol values have different flavors. The true weak reference behavior is
only supported by local symbols created with the
napi_create_symbol
function
or the JavaScript
Symbol()
constructor calls. Globally registered symbols
created with the
node_api_symbol_for
function or JavaScript
Symbol.for()
function calls remain always strong references because the garbage collector
does not collect them. The same is true for well-known symbols such as
Symbol.iterator
. They are also never collected by the garbage collector.
References can be created with an initial reference count. The count can
then be modified through
napi_reference_ref
and
napi_reference_unref
. If an object is collected while the count
for a reference is 0, all subsequent calls to
get the object associated with the reference
napi_get_reference_value
will return
NULL
for the returned
napi_value
. An attempt to call
napi_reference_ref
for a reference whose object has been collected
results in an error.
References must be deleted once they are no longer required by the addon. When
a reference is deleted, it will no longer prevent the corresponding object from
being collected. Failure to delete a persistent reference results in
a 'memory leak' with both the native memory for the persistent reference and
the corresponding object on the heap being retained forever.
There can be multiple persistent references created which refer to the same
object, each of which will either keep the object live or not based on its
individual count. Multiple persistent references to the same object
can result in unexpectedly keeping alive native memory. The native structures
for a persistent reference must be kept alive until finalizers for the
referenced object are executed. If a new persistent reference is created
for the same object, the finalizers for that object will not be
run and the native memory pointed by the earlier persistent reference
will not be freed. This can be avoided by calling
napi_delete_reference
in addition to
napi_reference_unref
when possible.
Change History:
Version 10 (
NAPI_VERSION
is defined as
10
or higher):
References can be created for all value types. The new supported value
types do not support weak reference semantic and the values of these types
are released when the reference count becomes 0 and cannot be accessed from
the reference anymore.
napi_create_reference
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_create_reference
napi_env
env
napi_value
value
uint32_t
initial_refcount
napi_ref
result
);
[in] env
: The environment that the API is invoked under.
[in] value
: The
napi_value
for which a reference is being created.
[in] initial_refcount
: Initial reference count for the new reference.
[out] result
napi_ref
pointing to the new reference.
Returns
napi_ok
if the API succeeded.
This API creates a new reference with the specified reference count
to the value passed in.
napi_delete_reference
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_delete_reference
napi_env
env
napi_ref
ref
);
[in] env
: The environment that the API is invoked under.
[in] ref
napi_ref
to be deleted.
Returns
napi_ok
if the API succeeded.
This API deletes the reference passed in.
This API can be called even if there is a pending JavaScript exception.
napi_reference_ref
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_reference_ref
napi_env
env
napi_ref
ref
uint32_t
result
);
[in] env
: The environment that the API is invoked under.
[in] ref
napi_ref
for which the reference count will be incremented.
[out] result
: The new reference count.
Returns
napi_ok
if the API succeeded.
This API increments the reference count for the reference
passed in and returns the resulting reference count.
napi_reference_unref
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_reference_unref
napi_env
env
napi_ref
ref
uint32_t
result
);
[in] env
: The environment that the API is invoked under.
[in] ref
napi_ref
for which the reference count will be decremented.
[out] result
: The new reference count.
Returns
napi_ok
if the API succeeded.
This API decrements the reference count for the reference
passed in and returns the resulting reference count.
napi_get_reference_value
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_get_reference_value
napi_env
env
napi_ref
ref
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] ref
: The
napi_ref
for which the corresponding value is
being requested.
[out] result
: The
napi_value
referenced by the
napi_ref
Returns
napi_ok
if the API succeeded.
If still valid, this API returns the
napi_value
representing the
JavaScript value associated with the
napi_ref
. Otherwise, result
will be
NULL
Cleanup on exit of the current Node.js environment
While a Node.js process typically releases all its resources when exiting,
embedders of Node.js, or future Worker support, may require addons to register
clean-up hooks that will be run once the current Node.js environment exits.
Node-API provides functions for registering and un-registering such callbacks.
When those callbacks are run, all resources that are being held by the addon
should be freed up.
napi_add_env_cleanup_hook
Added in: v10.2.0
N-API Version:
NODE_EXTERN napi_status
napi_add_env_cleanup_hook
node_api_basic_env
env
napi_cleanup_hook
fun
void
arg
);
Registers
fun
as a function to be run with the
arg
parameter once the
current Node.js environment exits.
A function can safely be specified multiple times with different
arg
values. In that case, it will be called multiple times as well.
Providing the same
fun
and
arg
values multiple times is not allowed
and will lead the process to abort.
The hooks will be called in reverse order, i.e. the most recently added one
will be called first.
Removing this hook can be done by using
napi_remove_env_cleanup_hook
Typically, that happens when the resource for which this hook was added
is being torn down anyway.
For asynchronous cleanup,
napi_add_async_cleanup_hook
is available.
napi_remove_env_cleanup_hook
Added in: v10.2.0
N-API Version:
NAPI_EXTERN napi_status
napi_remove_env_cleanup_hook
node_api_basic_env
env
void
fun
)(
void
arg
),
void
arg
);
Unregisters
fun
as a function to be run with the
arg
parameter once the
current Node.js environment exits. Both the argument and the function value
need to be exact matches.
The function must have originally been registered
with
napi_add_env_cleanup_hook
, otherwise the process will abort.
napi_add_async_cleanup_hook
Added in: v14.8.0, v12.19.0
N-API Version:
History
Version
Changes
v14.10.0, v12.19.0
Changed signature of the
hook
callback.
NAPI_EXTERN napi_status
napi_add_async_cleanup_hook
node_api_basic_env
env
napi_async_cleanup_hook
hook
void
arg
napi_async_cleanup_hook_handle
remove_handle
);
[in] env
: The environment that the API is invoked under.
[in] hook
: The function pointer to call at environment teardown.
[in] arg
: The pointer to pass to
hook
when it gets called.
[out] remove_handle
: Optional handle that refers to the asynchronous cleanup
hook.
Registers
hook
, which is a function of type
napi_async_cleanup_hook
, as
a function to be run with the
remove_handle
and
arg
parameters once the
current Node.js environment exits.
Unlike
napi_add_env_cleanup_hook
, the hook is allowed to be asynchronous.
Otherwise, behavior generally matches that of
napi_add_env_cleanup_hook
If
remove_handle
is not
NULL
, an opaque value will be stored in it
that must later be passed to
napi_remove_async_cleanup_hook
regardless of whether the hook has already been invoked.
Typically, that happens when the resource for which this hook was added
is being torn down anyway.
napi_remove_async_cleanup_hook
Added in: v14.8.0, v12.19.0
History
Version
Changes
v14.10.0, v12.19.0
Removed
env
parameter.
NAPI_EXTERN napi_status
napi_remove_async_cleanup_hook
napi_async_cleanup_hook_handle
remove_handle
);
[in] remove_handle
: The handle to an asynchronous cleanup hook that was
created with
napi_add_async_cleanup_hook
Unregisters the cleanup hook corresponding to
remove_handle
. This will prevent
the hook from being executed, unless it has already started executing.
This must be called on any
napi_async_cleanup_hook_handle
value obtained
from
napi_add_async_cleanup_hook
Finalization on the exit of the Node.js environment
The Node.js environment may be torn down at an arbitrary time as soon as
possible with JavaScript execution disallowed, like on the request of
worker.terminate()
. When the environment is being torn down, the
registered
napi_finalize
callbacks of JavaScript objects, thread-safe
functions and environment instance data are invoked immediately and
independently.
The invocation of
napi_finalize
callbacks is scheduled after the manually
registered cleanup hooks. In order to ensure a proper order of addon
finalization during environment shutdown to avoid use-after-free in the
napi_finalize
callback, addons should register a cleanup hook with
napi_add_env_cleanup_hook
and
napi_add_async_cleanup_hook
to manually
release the allocated resource in a proper order.
Module registration
Node-API modules are registered in a manner similar to other modules
except that instead of using the
NODE_MODULE
macro the following
is used:
NAPI_MODULE
NODE_GYP_MODULE_NAME
Init
The next difference is the signature for the
Init
method. For a Node-API
module it is as follows:
napi_value
Init
napi_env
env
napi_value
exports
);
The return value from
Init
is treated as the
exports
object for the module.
The
Init
method is passed an empty object via the
exports
parameter as a
convenience. If
Init
returns
NULL
, the parameter passed as
exports
is
exported by the module. Node-API modules cannot modify the
module
object but
can specify anything as the
exports
property of the module.
To add the method
hello
as a function so that it can be called as a method
provided by the addon:
napi_value
Init
napi_env
env
napi_value
exports
napi_status status
napi_property_descriptor desc
"hello"
NULL
Method
NULL
NULL
NULL
napi_writable
napi_enumerable
napi_configurable
NULL
};
status
napi_define_properties
env
exports
desc
);
if
status
!=
napi_ok
return
NULL
return
exports
To set a function to be returned by the
require()
for the addon:
napi_value
Init
napi_env
env
napi_value
exports
napi_value method
napi_status status
status
napi_create_function
env
"exports"
NAPI_AUTO_LENGTH
Method
NULL
method
);
if
status
!=
napi_ok
return
NULL
return
method
To define a class so that new instances can be created (often used with
Object wrap
):
// NOTE: partial example, not all referenced code is included
napi_value
Init
napi_env
env
napi_value
exports
napi_status status
napi_property_descriptor properties
[]
"value"
NULL
NULL
GetValue
SetValue
NULL
napi_writable
napi_configurable
NULL
},
DECLARE_NAPI_METHOD
"plusOne"
PlusOne
),
DECLARE_NAPI_METHOD
"multiply"
Multiply
),
};
napi_value cons
status
napi_define_class
env
"MyObject"
New
NULL
properties
cons
);
if
status
!=
napi_ok
return
NULL
status
napi_create_reference
env
cons
constructor
);
if
status
!=
napi_ok
return
NULL
status
napi_set_named_property
env
exports
"MyObject"
cons
);
if
status
!=
napi_ok
return
NULL
return
exports
You can also use the
NAPI_MODULE_INIT
macro, which acts as a shorthand
for
NAPI_MODULE
and defining an
Init
function:
NAPI_MODULE_INIT
/* napi_env env, napi_value exports */
napi_value answer
napi_status result
status
napi_create_int64
env
42
answer
);
if
status
!=
napi_ok
return
NULL
status
napi_set_named_property
env
exports
"answer"
answer
);
if
status
!=
napi_ok
return
NULL
return
exports
The parameters
env
and
exports
are provided to the body of the
NAPI_MODULE_INIT
macro.
All Node-API addons are context-aware, meaning they may be loaded multiple
times. There are a few design considerations when declaring such a module.
The documentation on
context-aware addons
provides more details.
The variables
env
and
exports
will be available inside the function body
following the macro invocation.
For more details on setting properties on objects, see the section on
Working with JavaScript properties
For more details on building addon modules in general, refer to the existing
API.
Working with JavaScript values
Node-API exposes a set of APIs to create all types of JavaScript values.
Some of these types are documented under
Section language types
of the
ECMAScript Language Specification
Fundamentally, these APIs are used to do one of the following:
Create a new JavaScript object
Convert from a primitive C type to a Node-API value
Convert from Node-API value to a primitive C type
Get global instances including
undefined
and
null
Node-API values are represented by the type
napi_value
Any Node-API call that requires a JavaScript value takes in a
napi_value
In some cases, the API does check the type of the
napi_value
up-front.
However, for better performance, it's better for the caller to make sure that
the
napi_value
in question is of the JavaScript type expected by the API.
Enum types
napi_key_collection_mode
Added in: v13.7.0, v12.17.0, v10.20.0
N-API Version:
typedef
enum
napi_key_include_prototypes
napi_key_own_only
napi_key_collection_mode
Describes the
Keys/Properties
filter enums:
napi_key_collection_mode
limits the range of collected properties.
napi_key_own_only
limits the collected properties to the given
object only.
napi_key_include_prototypes
will include all keys
of the objects's prototype chain as well.
napi_key_filter
Added in: v13.7.0, v12.17.0, v10.20.0
N-API Version:
typedef
enum
napi_key_all_properties
napi_key_writable
napi_key_enumerable
<<
napi_key_configurable
<<
napi_key_skip_strings
<<
napi_key_skip_symbols
<<
napi_key_filter
Property filter bit flag. This works with bit operators to build a composite filter.
napi_key_conversion
Added in: v13.7.0, v12.17.0, v10.20.0
N-API Version:
typedef
enum
napi_key_keep_numbers
napi_key_numbers_to_strings
napi_key_conversion
napi_key_numbers_to_strings
will convert integer indexes to
strings.
napi_key_keep_numbers
will return numbers for integer
indexes.
napi_valuetype
typedef
enum
// ES6 types (corresponds to typeof)
napi_undefined
napi_null
napi_boolean
napi_number
napi_string
napi_symbol
napi_object
napi_function
napi_external
napi_bigint
napi_valuetype
Describes the type of a
napi_value
. This generally corresponds to the types
described in
Section language types
of the ECMAScript Language Specification.
In addition to types in that section,
napi_valuetype
can also represent
Function
s and
Object
s with external data.
A JavaScript value of type
napi_external
appears in JavaScript as a plain
object such that no properties can be set on it, and no prototype.
napi_typedarray_type
History
Version
Changes
v25.4.0
Added
napi_float16_array
for Float16Array support.
typedef
enum
napi_int8_array
napi_uint8_array
napi_uint8_clamped_array
napi_int16_array
napi_uint16_array
napi_int32_array
napi_uint32_array
napi_float32_array
napi_float64_array
napi_bigint64_array
napi_biguint64_array
napi_float16_array
napi_typedarray_type
This represents the underlying binary scalar datatype of the
TypedArray
Elements of this enum correspond to
Section TypedArray objects
of the
ECMAScript Language Specification
Object creation functions
napi_create_array
Added in: v8.0.0
N-API Version:
napi_status
napi_create_array
napi_env
env
napi_value
result
[in] env
: The environment that the Node-API call is invoked under.
[out] result
: A
napi_value
representing a JavaScript
Array
Returns
napi_ok
if the API succeeded.
This API returns a Node-API value corresponding to a JavaScript
Array
type.
JavaScript arrays are described in
Section Array objects
of the ECMAScript Language Specification.
napi_create_array_with_length
Added in: v8.0.0
N-API Version:
napi_status
napi_create_array_with_length
napi_env
env
size_t
length
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] length
: The initial length of the
Array
[out] result
: A
napi_value
representing a JavaScript
Array
Returns
napi_ok
if the API succeeded.
This API returns a Node-API value corresponding to a JavaScript
Array
type.
The
Array
's length property is set to the passed-in length parameter.
However, the underlying buffer is not guaranteed to be pre-allocated by the VM
when the array is created. That behavior is left to the underlying VM
implementation. If the buffer must be a contiguous block of memory that can be
directly read and/or written via C, consider using
napi_create_external_arraybuffer
JavaScript arrays are described in
Section Array objects
of the ECMAScript Language Specification.
napi_create_arraybuffer
Added in: v8.0.0
N-API Version:
napi_status
napi_create_arraybuffer
napi_env
env
size_t
byte_length
void
**
data
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] length
: The length in bytes of the array buffer to create.
[out] data
: Pointer to the underlying byte buffer of the
ArrayBuffer
data
can optionally be ignored by passing
NULL
[out] result
: A
napi_value
representing a JavaScript
ArrayBuffer
Returns
napi_ok
if the API succeeded.
This API returns a Node-API value corresponding to a JavaScript
ArrayBuffer
ArrayBuffer
s are used to represent fixed-length binary data buffers. They are
normally used as a backing-buffer for
TypedArray
objects.
The
ArrayBuffer
allocated will have an underlying byte buffer whose size is
determined by the
length
parameter that's passed in.
The underlying buffer is optionally returned back to the caller in case the
caller wants to directly manipulate the buffer. This buffer can only be
written to directly from native code. To write to this buffer from JavaScript,
a typed array or
DataView
object would need to be created.
JavaScript
ArrayBuffer
objects are described in
Section ArrayBuffer objects
of the ECMAScript Language Specification.
napi_create_buffer
Added in: v8.0.0
N-API Version:
napi_status
napi_create_buffer
napi_env
env
size_t
size
void
**
data
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] size
: Size in bytes of the underlying buffer.
[out] data
: Raw pointer to the underlying buffer.
data
can optionally be ignored by passing
NULL
[out] result
: A
napi_value
representing a
node::Buffer
Returns
napi_ok
if the API succeeded.
This API allocates a
node::Buffer
object. While this is still a
fully-supported data structure, in most cases using a
TypedArray
will suffice.
napi_create_buffer_copy
Added in: v8.0.0
N-API Version:
napi_status
napi_create_buffer_copy
napi_env
env
size_t
length
const
void
data
void
**
result_data
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] size
: Size in bytes of the input buffer (should be the same as the size
of the new buffer).
[in] data
: Raw pointer to the underlying buffer to copy from.
[out] result_data
: Pointer to the new
Buffer
's underlying data buffer.
result_data
can optionally be ignored by passing
NULL
[out] result
: A
napi_value
representing a
node::Buffer
Returns
napi_ok
if the API succeeded.
This API allocates a
node::Buffer
object and initializes it with data copied
from the passed-in buffer. While this is still a fully-supported data
structure, in most cases using a
TypedArray
will suffice.
napi_create_date
Added in: v11.11.0, v10.17.0
N-API Version:
napi_status
napi_create_date
napi_env
env
double
time
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] time
: ECMAScript time value in milliseconds since 01 January, 1970 UTC.
[out] result
: A
napi_value
representing a JavaScript
Date
Returns
napi_ok
if the API succeeded.
This API does not observe leap seconds; they are ignored, as
ECMAScript aligns with POSIX time specification.
This API allocates a JavaScript
Date
object.
JavaScript
Date
objects are described in
Section Date objects
of the ECMAScript Language Specification.
napi_create_external
Added in: v8.0.0
N-API Version:
napi_status
napi_create_external
napi_env
env
void
data
napi_finalize
finalize_cb
void
finalize_hint
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] data
: Raw pointer to the external data.
[in] finalize_cb
: Optional callback to call when the external value is being
collected.
napi_finalize
provides more details.
[in] finalize_hint
: Optional hint to pass to the finalize callback during
collection.
[out] result
: A
napi_value
representing an external value.
Returns
napi_ok
if the API succeeded.
This API allocates a JavaScript value with external data attached to it. This
is used to pass external data through JavaScript code, so it can be retrieved
later by native code using
napi_get_value_external
The API adds a
napi_finalize
callback which will be called when the JavaScript
object just created has been garbage collected.
The created value is not an object, and therefore does not support additional
properties. It is considered a distinct value type: calling
napi_typeof()
with
an external value yields
napi_external
napi_create_external_arraybuffer
Added in: v8.0.0
N-API Version:
napi_status
napi_create_external_arraybuffer
napi_env
env
void
external_data
size_t
byte_length
napi_finalize
finalize_cb
void
finalize_hint
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] external_data
: Pointer to the underlying byte buffer of the
ArrayBuffer
[in] byte_length
: The length in bytes of the underlying buffer.
[in] finalize_cb
: Optional callback to call when the
ArrayBuffer
is being
collected.
napi_finalize
provides more details.
[in] finalize_hint
: Optional hint to pass to the finalize callback during
collection.
[out] result
: A
napi_value
representing a JavaScript
ArrayBuffer
Returns
napi_ok
if the API succeeded.
Some runtimes other than Node.js have dropped support for external buffers
On runtimes other than Node.js this method may return
napi_no_external_buffers_allowed
to indicate that external
buffers are not supported. One such runtime is Electron as
described in this issue
electron/issues/35801
In order to maintain broadest compatibility with all runtimes
you may define
NODE_API_NO_EXTERNAL_BUFFERS_ALLOWED
in your addon before
includes for the node-api headers. Doing so will hide the 2 functions
that create external buffers. This will ensure a compilation error
occurs if you accidentally use one of these methods.
This API returns a Node-API value corresponding to a JavaScript
ArrayBuffer
The underlying byte buffer of the
ArrayBuffer
is externally allocated and
managed. The caller must ensure that the byte buffer remains valid until the
finalize callback is called.
The API adds a
napi_finalize
callback which will be called when the JavaScript
object just created has been garbage collected.
JavaScript
ArrayBuffer
s are described in
Section ArrayBuffer objects
of the ECMAScript Language Specification.
napi_create_external_buffer
Added in: v8.0.0
N-API Version:
napi_status
napi_create_external_buffer
napi_env
env
size_t
length
void
data
napi_finalize
finalize_cb
void
finalize_hint
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] length
: Size in bytes of the input buffer (should be the same as the
size of the new buffer).
[in] data
: Raw pointer to the underlying buffer to expose to JavaScript.
[in] finalize_cb
: Optional callback to call when the
ArrayBuffer
is being
collected.
napi_finalize
provides more details.
[in] finalize_hint
: Optional hint to pass to the finalize callback during
collection.
[out] result
: A
napi_value
representing a
node::Buffer
Returns
napi_ok
if the API succeeded.
Some runtimes other than Node.js have dropped support for external buffers
On runtimes other than Node.js this method may return
napi_no_external_buffers_allowed
to indicate that external
buffers are not supported. One such runtime is Electron as
described in this issue
electron/issues/35801
In order to maintain broadest compatibility with all runtimes
you may define
NODE_API_NO_EXTERNAL_BUFFERS_ALLOWED
in your addon before
includes for the node-api headers. Doing so will hide the 2 functions
that create external buffers. This will ensure a compilation error
occurs if you accidentally use one of these methods.
This API allocates a
node::Buffer
object and initializes it with data
backed by the passed in buffer. While this is still a fully-supported data
structure, in most cases using a
TypedArray
will suffice.
The API adds a
napi_finalize
callback which will be called when the JavaScript
object just created has been garbage collected.
For Node.js >=4
Buffers
are
Uint8Array
s.
napi_create_object
Added in: v8.0.0
N-API Version:
napi_status
napi_create_object
napi_env
env
napi_value
result
[in] env
: The environment that the API is invoked under.
[out] result
: A
napi_value
representing a JavaScript
Object
Returns
napi_ok
if the API succeeded.
This API allocates a default JavaScript
Object
It is the equivalent of doing
new Object()
in JavaScript.
The JavaScript
Object
type is described in
Section object type
of the
ECMAScript Language Specification.
node_api_create_object_with_properties
Added in: v25.2.0
Stability: 1 - Experimental
napi_status
node_api_create_object_with_properties
napi_env
env
napi_value
prototype_or_null
const
napi_value
property_names
const
napi_value
property_values
size_t
property_count
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] prototype_or_null
: The prototype object for the new object. Can be a
napi_value
representing a JavaScript object to use as the prototype, a
napi_value
representing JavaScript
null
, or a
nullptr
that will be converted to
null
[in] property_names
: Array of
napi_value
representing the property names.
[in] property_values
: Array of
napi_value
representing the property values.
[in] property_count
: Number of properties in the arrays.
[out] result
: A
napi_value
representing a JavaScript
Object
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
Object
with the specified prototype and
properties. This is more efficient than calling
napi_create_object
followed
by multiple
napi_set_property
calls, as it can create the object with all
properties atomically, avoiding potential V8 map transitions.
The arrays
property_names
and
property_values
must have the same length
specified by
property_count
. The properties are added to the object in the
order they appear in the arrays.
napi_create_symbol
Added in: v8.0.0
N-API Version:
napi_status
napi_create_symbol
napi_env
env
napi_value
description
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] description
: Optional
napi_value
which refers to a JavaScript
string
to be set as the description for the symbol.
[out] result
: A
napi_value
representing a JavaScript
symbol
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
symbol
value from a UTF8-encoded C string.
The JavaScript
symbol
type is described in
Section symbol type
of the ECMAScript Language Specification.
node_api_symbol_for
Added in: v17.5.0, v16.15.0
N-API Version:
napi_status
node_api_symbol_for
napi_env
env
const
char
utf8description
size_t
length
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] utf8description
: UTF-8 C string representing the text to be used as the
description for the symbol.
[in] length
: The length of the description string in bytes, or
NAPI_AUTO_LENGTH
if it is null-terminated.
[out] result
: A
napi_value
representing a JavaScript
symbol
Returns
napi_ok
if the API succeeded.
This API searches in the global registry for an existing symbol with the given
description. If the symbol already exists it will be returned, otherwise a new
symbol will be created in the registry.
The JavaScript
symbol
type is described in
Section symbol type
of the ECMAScript
Language Specification.
napi_create_typedarray
Added in: v8.0.0
N-API Version:
napi_status
napi_create_typedarray
napi_env
env
napi_typedarray_type
type
size_t
length
napi_value
arraybuffer
size_t
byte_offset
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] type
: Scalar datatype of the elements within the
TypedArray
[in] length
: Number of elements in the
TypedArray
[in] arraybuffer
ArrayBuffer
underlying the typed array.
[in] byte_offset
: The byte offset within the
ArrayBuffer
from which to
start projecting the
TypedArray
[out] result
: A
napi_value
representing a JavaScript
TypedArray
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
TypedArray
object over an existing
ArrayBuffer
TypedArray
objects provide an array-like view over an
underlying data buffer where each element has the same underlying binary scalar
datatype.
It's required that
(length * size_of_element) + byte_offset
should
be <= the size in bytes of the array passed in. If not, a
RangeError
exception
is raised.
JavaScript
TypedArray
objects are described in
Section TypedArray objects
of the ECMAScript Language Specification.
node_api_create_buffer_from_arraybuffer
Added in: v23.0.0, v22.12.0
N-API Version:
10
napi_status NAPI_CDECL
node_api_create_buffer_from_arraybuffer
napi_env
env
napi_value
arraybuffer
size_t
byte_offset
size_t
byte_length
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] arraybuffer
: The
ArrayBuffer
from which the buffer will be created.
[in] byte_offset
: The byte offset within the
ArrayBuffer
from which to start creating the buffer.
[in] byte_length
: The length in bytes of the buffer to be created from the
ArrayBuffer
[out] result
: A
napi_value
representing the created JavaScript
Buffer
object.
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
Buffer
object from an existing
ArrayBuffer
The
Buffer
object is a Node.js-specific class that provides a way to work with binary data directly in JavaScript.
The byte range
[byte_offset, byte_offset + byte_length)
must be within the bounds of the
ArrayBuffer
. If
byte_offset + byte_length
exceeds the size of the
ArrayBuffer
, a
RangeError
exception is raised.
napi_create_dataview
Added in: v8.3.0
N-API Version:
History
Version
Changes
v25.4.0
Added support for
SharedArrayBuffer
napi_status
napi_create_dataview
napi_env
env
size_t
byte_length
napi_value
arraybuffer
size_t
byte_offset
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] length
: Number of elements in the
DataView
[in] arraybuffer
ArrayBuffer
or
SharedArrayBuffer
underlying the
DataView
[in] byte_offset
: The byte offset within the
ArrayBuffer
from which to
start projecting the
DataView
[out] result
: A
napi_value
representing a JavaScript
DataView
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
DataView
object over an existing
ArrayBuffer
or
SharedArrayBuffer
DataView
objects provide an array-like view over an
underlying data buffer, but one which allows items of different size and type in
the
ArrayBuffer
or
SharedArrayBuffer
It is required that
byte_length + byte_offset
is less than or equal to the
size in bytes of the array passed in. If not, a
RangeError
exception is
raised.
JavaScript
DataView
objects are described in
Section DataView objects
of the ECMAScript Language Specification.
Functions to convert from C types to Node-API
napi_create_int32
Added in: v8.4.0
N-API Version:
napi_status
napi_create_int32
napi_env
env
int32_t
value
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] value
: Integer value to be represented in JavaScript.
[out] result
: A
napi_value
representing a JavaScript
number
Returns
napi_ok
if the API succeeded.
This API is used to convert from the C
int32_t
type to the JavaScript
number
type.
The JavaScript
number
type is described in
Section number type
of the ECMAScript Language Specification.
napi_create_uint32
Added in: v8.4.0
N-API Version:
napi_status
napi_create_uint32
napi_env
env
uint32_t
value
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] value
: Unsigned integer value to be represented in JavaScript.
[out] result
: A
napi_value
representing a JavaScript
number
Returns
napi_ok
if the API succeeded.
This API is used to convert from the C
uint32_t
type to the JavaScript
number
type.
The JavaScript
number
type is described in
Section number type
of the ECMAScript Language Specification.
napi_create_int64
Added in: v8.4.0
N-API Version:
napi_status
napi_create_int64
napi_env
env
int64_t
value
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] value
: Integer value to be represented in JavaScript.
[out] result
: A
napi_value
representing a JavaScript
number
Returns
napi_ok
if the API succeeded.
This API is used to convert from the C
int64_t
type to the JavaScript
number
type.
The JavaScript
number
type is described in
Section number type
of the ECMAScript Language Specification. Note the complete range of
int64_t
cannot be represented with full precision in JavaScript. Integer values
outside the range of
Number.MIN_SAFE_INTEGER
-(2**53 - 1)
Number.MAX_SAFE_INTEGER
(2**53 - 1)
will lose precision.
napi_create_double
Added in: v8.4.0
N-API Version:
napi_status
napi_create_double
napi_env
env
double
value
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] value
: Double-precision value to be represented in JavaScript.
[out] result
: A
napi_value
representing a JavaScript
number
Returns
napi_ok
if the API succeeded.
This API is used to convert from the C
double
type to the JavaScript
number
type.
The JavaScript
number
type is described in
Section number type
of the ECMAScript Language Specification.
napi_create_bigint_int64
Added in: v10.7.0
N-API Version:
napi_status
napi_create_bigint_int64
napi_env
env
int64_t
value
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] value
: Integer value to be represented in JavaScript.
[out] result
: A
napi_value
representing a JavaScript
BigInt
Returns
napi_ok
if the API succeeded.
This API converts the C
int64_t
type to the JavaScript
BigInt
type.
napi_create_bigint_uint64
Added in: v10.7.0
N-API Version:
napi_status
napi_create_bigint_uint64
napi_env
env
uint64_t
value
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] value
: Unsigned integer value to be represented in JavaScript.
[out] result
: A
napi_value
representing a JavaScript
BigInt
Returns
napi_ok
if the API succeeded.
This API converts the C
uint64_t
type to the JavaScript
BigInt
type.
napi_create_bigint_words
Added in: v10.7.0
N-API Version:
napi_status
napi_create_bigint_words
napi_env
env
int
sign_bit
size_t
word_count
const
uint64_t
words
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] sign_bit
: Determines if the resulting
BigInt
will be positive or
negative.
[in] word_count
: The length of the
words
array.
[in] words
: An array of
uint64_t
little-endian 64-bit words.
[out] result
: A
napi_value
representing a JavaScript
BigInt
Returns
napi_ok
if the API succeeded.
This API converts an array of unsigned 64-bit words into a single
BigInt
value.
The resulting
BigInt
is calculated as: (–1)
sign_bit
words[0]
× (2
64
words[1]
× (2
64
+ …)
napi_create_string_latin1
Added in: v8.0.0
N-API Version:
napi_status
napi_create_string_latin1
napi_env
env
const
char
str
size_t
length
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] str
: Character buffer representing an ISO-8859-1-encoded string.
[in] length
: The length of the string in bytes, or
NAPI_AUTO_LENGTH
if it
is null-terminated.
[out] result
: A
napi_value
representing a JavaScript
string
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
string
value from an ISO-8859-1-encoded C
string. The native string is copied.
The JavaScript
string
type is described in
Section string type
of the ECMAScript Language Specification.
node_api_create_external_string_latin1
Added in: v20.4.0, v18.18.0
N-API Version:
10
napi_status
node_api_create_external_string_latin1
napi_env
env
char
str
size_t
length
napi_finalize
finalize_callback
void
finalize_hint
napi_value
result
bool
copied
);
[in] env
: The environment that the API is invoked under.
[in] str
: Character buffer representing an ISO-8859-1-encoded string.
[in] length
: The length of the string in bytes, or
NAPI_AUTO_LENGTH
if it
is null-terminated.
[in] finalize_callback
: The function to call when the string is being
collected. The function will be called with the following parameters:
[in] env
: The environment in which the add-on is running. This value
may be null if the string is being collected as part of the termination
of the worker or the main Node.js instance.
[in] data
: This is the value
str
as a
void*
pointer.
[in] finalize_hint
: This is the value
finalize_hint
that was given
to the API.
napi_finalize
provides more details.
This parameter is optional. Passing a null value means that the add-on
doesn't need to be notified when the corresponding JavaScript string is
collected.
[in] finalize_hint
: Optional hint to pass to the finalize callback during
collection.
[out] result
: A
napi_value
representing a JavaScript
string
[out] copied
: Whether the string was copied. If it was, the finalizer will
already have been invoked to destroy
str
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
string
value from an ISO-8859-1-encoded C
string. The native string may not be copied and must thus exist for the entire
life cycle of the JavaScript value.
The JavaScript
string
type is described in
Section string type
of the ECMAScript Language Specification.
napi_create_string_utf16
Added in: v8.0.0
N-API Version:
napi_status
napi_create_string_utf16
napi_env
env
const
char16_t
str
size_t
length
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] str
: Character buffer representing a UTF16-LE-encoded string.
[in] length
: The length of the string in two-byte code units, or
NAPI_AUTO_LENGTH
if it is null-terminated.
[out] result
: A
napi_value
representing a JavaScript
string
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
string
value from a UTF16-LE-encoded C string.
The native string is copied.
The JavaScript
string
type is described in
Section string type
of the ECMAScript Language Specification.
node_api_create_external_string_utf16
Added in: v20.4.0, v18.18.0
N-API Version:
10
napi_status
node_api_create_external_string_utf16
napi_env
env
char16_t
str
size_t
length
napi_finalize
finalize_callback
void
finalize_hint
napi_value
result
bool
copied
);
[in] env
: The environment that the API is invoked under.
[in] str
: Character buffer representing a UTF16-LE-encoded string.
[in] length
: The length of the string in two-byte code units, or
NAPI_AUTO_LENGTH
if it is null-terminated.
[in] finalize_callback
: The function to call when the string is being
collected. The function will be called with the following parameters:
[in] env
: The environment in which the add-on is running. This value
may be null if the string is being collected as part of the termination
of the worker or the main Node.js instance.
[in] data
: This is the value
str
as a
void*
pointer.
[in] finalize_hint
: This is the value
finalize_hint
that was given
to the API.
napi_finalize
provides more details.
This parameter is optional. Passing a null value means that the add-on
doesn't need to be notified when the corresponding JavaScript string is
collected.
[in] finalize_hint
: Optional hint to pass to the finalize callback during
collection.
[out] result
: A
napi_value
representing a JavaScript
string
[out] copied
: Whether the string was copied. If it was, the finalizer will
already have been invoked to destroy
str
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
string
value from a UTF16-LE-encoded C string.
The native string may not be copied and must thus exist for the entire life
cycle of the JavaScript value.
The JavaScript
string
type is described in
Section string type
of the ECMAScript Language Specification.
napi_create_string_utf8
Added in: v8.0.0
N-API Version:
napi_status
napi_create_string_utf8
napi_env
env
const
char
str
size_t
length
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] str
: Character buffer representing a UTF8-encoded string.
[in] length
: The length of the string in bytes, or
NAPI_AUTO_LENGTH
if it
is null-terminated.
[out] result
: A
napi_value
representing a JavaScript
string
Returns
napi_ok
if the API succeeded.
This API creates a JavaScript
string
value from a UTF8-encoded C string.
The native string is copied.
The JavaScript
string
type is described in
Section string type
of the ECMAScript Language Specification.
Functions to create optimized property keys
Many JavaScript engines including V8 use internalized strings as keys
to set and get property values. They typically use a hash table to create
and lookup such strings. While it adds some cost per key creation, it improves
the performance after that by enabling comparison of string pointers instead
of the whole strings.
If a new JavaScript string is intended to be used as a property key, then for
some JavaScript engines it will be more efficient to use the functions in this
section. Otherwise, use the
napi_create_string_utf8
or
node_api_create_external_string_utf8
series functions as there may be
additional overhead in creating/storing strings with the property key
creation methods.
node_api_create_property_key_latin1
Added in: v22.9.0, v20.18.0
N-API Version:
10
napi_status NAPI_CDECL
node_api_create_property_key_latin1
napi_env
env
const
char
str
size_t
length
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] str
: Character buffer representing an ISO-8859-1-encoded string.
[in] length
: The length of the string in bytes, or
NAPI_AUTO_LENGTH
if it
is null-terminated.
[out] result
: A
napi_value
representing an optimized JavaScript
string
to be used as a property key for objects.
Returns
napi_ok
if the API succeeded.
This API creates an optimized JavaScript
string
value from
an ISO-8859-1-encoded C string to be used as a property key for objects.
The native string is copied. In contrast with
napi_create_string_latin1
subsequent calls to this function with the same
str
pointer may benefit from a speedup
in the creation of the requested
napi_value
, depending on the engine.
The JavaScript
string
type is described in
Section string type
of the ECMAScript Language Specification.
node_api_create_property_key_utf16
Added in: v21.7.0, v20.12.0
N-API Version:
10
napi_status NAPI_CDECL
node_api_create_property_key_utf16
napi_env
env
const
char16_t
str
size_t
length
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] str
: Character buffer representing a UTF16-LE-encoded string.
[in] length
: The length of the string in two-byte code units, or
NAPI_AUTO_LENGTH
if it is null-terminated.
[out] result
: A
napi_value
representing an optimized JavaScript
string
to be used as a property key for objects.
Returns
napi_ok
if the API succeeded.
This API creates an optimized JavaScript
string
value from
a UTF16-LE-encoded C string to be used as a property key for objects.
The native string is copied.
The JavaScript
string
type is described in
Section string type
of the ECMAScript Language Specification.
node_api_create_property_key_utf8
Added in: v22.9.0, v20.18.0
N-API Version:
10
napi_status NAPI_CDECL
node_api_create_property_key_utf8
napi_env
env
const
char
str
size_t
length
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] str
: Character buffer representing a UTF8-encoded string.
[in] length
: The length of the string in two-byte code units, or
NAPI_AUTO_LENGTH
if it is null-terminated.
[out] result
: A
napi_value
representing an optimized JavaScript
string
to be used as a property key for objects.
Returns
napi_ok
if the API succeeded.
This API creates an optimized JavaScript
string
value from
a UTF8-encoded C string to be used as a property key for objects.
The native string is copied.
The JavaScript
string
type is described in
Section string type
of the ECMAScript Language Specification.
Functions to convert from Node-API to C types
napi_get_array_length
Added in: v8.0.0
N-API Version:
napi_status
napi_get_array_length
napi_env
env
napi_value
value
uint32_t
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing the JavaScript
Array
whose length is
being queried.
[out] result
uint32
representing length of the array.
Returns
napi_ok
if the API succeeded.
This API returns the length of an array.
Array
length is described in
Section Array instance length
of the ECMAScript Language
Specification.
napi_get_arraybuffer_info
Added in: v8.0.0
N-API Version:
History
Version
Changes
v24.9.0
Added support for
SharedArrayBuffer
napi_status
napi_get_arraybuffer_info
napi_env
env
napi_value
arraybuffer
void
**
data
size_t
byte_length
[in] env
: The environment that the API is invoked under.
[in] arraybuffer
napi_value
representing the
ArrayBuffer
or
SharedArrayBuffer
being queried.
[out] data
: The underlying data buffer of the
ArrayBuffer
or
SharedArrayBuffer
is
, this may be
NULL
or any other pointer value.
[out] byte_length
: Length in bytes of the underlying data buffer.
Returns
napi_ok
if the API succeeded.
This API is used to retrieve the underlying data buffer of an
ArrayBuffer
or
SharedArrayBuffer
and its length.
WARNING
: Use caution while using this API. The lifetime of the underlying data
buffer is managed by the
ArrayBuffer
or
SharedArrayBuffer
even after it's returned. A
possible safe way to use this API is in conjunction with
napi_create_reference
, which can be used to guarantee control over the
lifetime of the
ArrayBuffer
or
SharedArrayBuffer
. It's also safe to use the returned data buffer
within the same callback as long as there are no calls to other APIs that might
trigger a GC.
napi_get_buffer_info
Added in: v8.0.0
N-API Version:
napi_status
napi_get_buffer_info
napi_env
env
napi_value
value
void
**
data
size_t
length
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing the
node::Buffer
or
Uint8Array
being queried.
[out] data
: The underlying data buffer of the
node::Buffer
or
Uint8Array
. If length is
, this may be
NULL
or any other pointer value.
[out] length
: Length in bytes of the underlying data buffer.
Returns
napi_ok
if the API succeeded.
This method returns the identical
data
and
byte_length
as
napi_get_typedarray_info
. And
napi_get_typedarray_info
accepts a
node::Buffer
(a Uint8Array) as the value too.
This API is used to retrieve the underlying data buffer of a
node::Buffer
and its length.
Warning
: Use caution while using this API since the underlying data buffer's
lifetime is not guaranteed if it's managed by the VM.
napi_get_prototype
Added in: v8.0.0
N-API Version:
napi_status
napi_get_prototype
napi_env
env
napi_value
object
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] object
napi_value
representing JavaScript
Object
whose prototype
to return. This returns the equivalent of
Object.getPrototypeOf
(which is
not the same as the function's
prototype
property).
[out] result
napi_value
representing prototype of the given object.
Returns
napi_ok
if the API succeeded.
napi_get_typedarray_info
Added in: v8.0.0
N-API Version:
napi_status
napi_get_typedarray_info
napi_env
env
napi_value
typedarray
napi_typedarray_type
type
size_t
length
void
**
data
napi_value
arraybuffer
size_t
byte_offset
[in] env
: The environment that the API is invoked under.
[in] typedarray
napi_value
representing the
TypedArray
whose
properties to query.
[out] type
: Scalar datatype of the elements within the
TypedArray
[out] length
: The number of elements in the
TypedArray
[out] data
: The data buffer underlying the
TypedArray
adjusted by
the
byte_offset
value so that it points to the first element in the
TypedArray
. If the length of the array is
, this may be
NULL
or
any other pointer value.
[out] arraybuffer
: The
ArrayBuffer
underlying the
TypedArray
[out] byte_offset
: The byte offset within the underlying native array
at which the first element of the arrays is located. The value for the data
parameter has already been adjusted so that data points to the first element
in the array. Therefore, the first byte of the native array would be at
data - byte_offset
Returns
napi_ok
if the API succeeded.
This API returns various properties of a typed array.
Any of the out parameters may be
NULL
if that property is unneeded.
Warning
: Use caution while using this API since the underlying data buffer
is managed by the VM.
napi_get_dataview_info
Added in: v8.3.0
N-API Version:
napi_status
napi_get_dataview_info
napi_env
env
napi_value
dataview
size_t
byte_length
void
**
data
napi_value
arraybuffer
size_t
byte_offset
[in] env
: The environment that the API is invoked under.
[in] dataview
napi_value
representing the
DataView
whose
properties to query.
[out] byte_length
: Number of bytes in the
DataView
[out] data
: The data buffer underlying the
DataView
If byte_length is
, this may be
NULL
or any other pointer value.
[out] arraybuffer
ArrayBuffer
underlying the
DataView
[out] byte_offset
: The byte offset within the data buffer from which
to start projecting the
DataView
Returns
napi_ok
if the API succeeded.
Any of the out parameters may be
NULL
if that property is unneeded.
This API returns various properties of a
DataView
napi_get_date_value
Added in: v11.11.0, v10.17.0
N-API Version:
napi_status
napi_get_date_value
napi_env
env
napi_value
value
double
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing a JavaScript
Date
[out] result
: Time value as a
double
represented as milliseconds since
midnight at the beginning of 01 January, 1970 UTC.
This API does not observe leap seconds; they are ignored, as
ECMAScript aligns with POSIX time specification.
Returns
napi_ok
if the API succeeded. If a non-date
napi_value
is passed
in it returns
napi_date_expected
This API returns the C double primitive of time value for the given JavaScript
Date
napi_get_value_bool
Added in: v8.0.0
N-API Version:
napi_status
napi_get_value_bool
napi_env
env
napi_value
value
bool
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript
Boolean
[out] result
: C boolean primitive equivalent of the given JavaScript
Boolean
Returns
napi_ok
if the API succeeded. If a non-boolean
napi_value
is
passed in it returns
napi_boolean_expected
This API returns the C boolean primitive equivalent of the given JavaScript
Boolean
napi_get_value_double
Added in: v8.0.0
N-API Version:
napi_status
napi_get_value_double
napi_env
env
napi_value
value
double
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript
number
[out] result
: C double primitive equivalent of the given JavaScript
number
Returns
napi_ok
if the API succeeded. If a non-number
napi_value
is passed
in it returns
napi_number_expected
This API returns the C double primitive equivalent of the given JavaScript
number
napi_get_value_bigint_int64
Added in: v10.7.0
N-API Version:
napi_status
napi_get_value_bigint_int64
napi_env
env
napi_value
value
int64_t
result
bool
lossless
);
[in] env
: The environment that the API is invoked under
[in] value
napi_value
representing JavaScript
BigInt
[out] result
: C
int64_t
primitive equivalent of the given JavaScript
BigInt
[out] lossless
: Indicates whether the
BigInt
value was converted
losslessly.
Returns
napi_ok
if the API succeeded. If a non-
BigInt
is passed in it
returns
napi_bigint_expected
This API returns the C
int64_t
primitive equivalent of the given JavaScript
BigInt
. If needed it will truncate the value, setting
lossless
to
false
napi_get_value_bigint_uint64
Added in: v10.7.0
N-API Version:
napi_status
napi_get_value_bigint_uint64
napi_env
env
napi_value
value
uint64_t
result
bool
lossless
);
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript
BigInt
[out] result
: C
uint64_t
primitive equivalent of the given JavaScript
BigInt
[out] lossless
: Indicates whether the
BigInt
value was converted
losslessly.
Returns
napi_ok
if the API succeeded. If a non-
BigInt
is passed in it
returns
napi_bigint_expected
This API returns the C
uint64_t
primitive equivalent of the given JavaScript
BigInt
. If needed it will truncate the value, setting
lossless
to
false
napi_get_value_bigint_words
Added in: v10.7.0
N-API Version:
napi_status
napi_get_value_bigint_words
napi_env
env
napi_value
value
int
sign_bit
size_t
word_count
uint64_t
words
);
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript
BigInt
[out] sign_bit
: Integer representing if the JavaScript
BigInt
is positive
or negative.
[in/out] word_count
: Must be initialized to the length of the
words
array. Upon return, it will be set to the actual number of words that
would be needed to store this
BigInt
[out] words
: Pointer to a pre-allocated 64-bit word array.
Returns
napi_ok
if the API succeeded.
This API converts a single
BigInt
value into a sign bit, 64-bit little-endian
array, and the number of elements in the array.
sign_bit
and
words
may be
both set to
NULL
, in order to get only
word_count
napi_get_value_external
Added in: v8.0.0
N-API Version:
napi_status
napi_get_value_external
napi_env
env
napi_value
value
void
**
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript external value.
[out] result
: Pointer to the data wrapped by the JavaScript external value.
Returns
napi_ok
if the API succeeded. If a non-external
napi_value
is
passed in it returns
napi_invalid_arg
This API retrieves the external data pointer that was previously passed to
napi_create_external()
napi_get_value_int32
Added in: v8.0.0
N-API Version:
napi_status
napi_get_value_int32
napi_env
env
napi_value
value
int32_t
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript
number
[out] result
: C
int32
primitive equivalent of the given JavaScript
number
Returns
napi_ok
if the API succeeded. If a non-number
napi_value
is passed in
napi_number_expected
This API returns the C
int32
primitive equivalent
of the given JavaScript
number
If the number exceeds the range of the 32 bit integer, then the result is
truncated to the equivalent of the bottom 32 bits. This can result in a large
positive number becoming a negative number if the value is > 2
31
- 1.
Non-finite number values (
NaN
+Infinity
, or
-Infinity
) set the
result to zero.
napi_get_value_int64
Added in: v8.0.0
N-API Version:
napi_status
napi_get_value_int64
napi_env
env
napi_value
value
int64_t
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript
number
[out] result
: C
int64
primitive equivalent of the given JavaScript
number
Returns
napi_ok
if the API succeeded. If a non-number
napi_value
is passed in it returns
napi_number_expected
This API returns the C
int64
primitive equivalent of the given JavaScript
number
number
values outside the range of
Number.MIN_SAFE_INTEGER
-(2**53 - 1)
Number.MAX_SAFE_INTEGER
(2**53 - 1)
will lose
precision.
Non-finite number values (
NaN
+Infinity
, or
-Infinity
) set the
result to zero.
napi_get_value_string_latin1
Added in: v8.0.0
N-API Version:
napi_status
napi_get_value_string_latin1
napi_env
env
napi_value
value
char
buf
size_t
bufsize
size_t
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript string.
[in] buf
: Buffer to write the ISO-8859-1-encoded string into. If
NULL
is
passed in, the length of the string in bytes and excluding the null terminator
is returned in
result
[in] bufsize
: Size of the destination buffer. When this value is
insufficient, the returned string is truncated and null-terminated.
If this value is zero, then the string is not returned and no changes are done
to the buffer.
[out] result
: Number of bytes copied into the buffer, excluding the null
terminator.
Returns
napi_ok
if the API succeeded. If a non-
string
napi_value
is passed in it returns
napi_string_expected
This API returns the ISO-8859-1-encoded string corresponding the value passed
in.
napi_get_value_string_utf8
Added in: v8.0.0
N-API Version:
napi_status
napi_get_value_string_utf8
napi_env
env
napi_value
value
char
buf
size_t
bufsize
size_t
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript string.
[in] buf
: Buffer to write the UTF8-encoded string into. If
NULL
is passed
in, the length of the string in bytes and excluding the null terminator is
returned in
result
[in] bufsize
: Size of the destination buffer. When this value is
insufficient, the returned string is truncated and null-terminated.
If this value is zero, then the string is not returned and no changes are done
to the buffer.
[out] result
: Number of bytes copied into the buffer, excluding the null
terminator.
Returns
napi_ok
if the API succeeded. If a non-
string
napi_value
is passed in it returns
napi_string_expected
This API returns the UTF8-encoded string corresponding the value passed in.
napi_get_value_string_utf16
Added in: v8.0.0
N-API Version:
napi_status
napi_get_value_string_utf16
napi_env
env
napi_value
value
char16_t
buf
size_t
bufsize
size_t
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript string.
[in] buf
: Buffer to write the UTF16-LE-encoded string into. If
NULL
is
passed in, the length of the string in 2-byte code units and excluding the
null terminator is returned.
[in] bufsize
: Size of the destination buffer. When this value is
insufficient, the returned string is truncated and null-terminated.
If this value is zero, then the string is not returned and no changes are done
to the buffer.
[out] result
: Number of 2-byte code units copied into the buffer, excluding
the null terminator.
Returns
napi_ok
if the API succeeded. If a non-
string
napi_value
is passed in it returns
napi_string_expected
This API returns the UTF16-encoded string corresponding the value passed in.
napi_get_value_uint32
Added in: v8.0.0
N-API Version:
napi_status
napi_get_value_uint32
napi_env
env
napi_value
value
uint32_t
result
[in] env
: The environment that the API is invoked under.
[in] value
napi_value
representing JavaScript
number
[out] result
: C primitive equivalent of the given
napi_value
as a
uint32_t
Returns
napi_ok
if the API succeeded. If a non-number
napi_value
is passed in it returns
napi_number_expected
This API returns the C primitive equivalent of the given
napi_value
as a
uint32_t
Functions to get global instances
napi_get_boolean
Added in: v8.0.0
N-API Version:
napi_status
napi_get_boolean
napi_env
env
bool
value
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] value
: The value of the boolean to retrieve.
[out] result
napi_value
representing JavaScript
Boolean
singleton to
retrieve.
Returns
napi_ok
if the API succeeded.
This API is used to return the JavaScript singleton object that is used to
represent the given boolean value.
napi_get_global
Added in: v8.0.0
N-API Version:
napi_status
napi_get_global
napi_env
env
napi_value
result
[in] env
: The environment that the API is invoked under.
[out] result
napi_value
representing JavaScript
global
object.
Returns
napi_ok
if the API succeeded.
This API returns the
global
object.
napi_get_null
Added in: v8.0.0
N-API Version:
napi_status
napi_get_null
napi_env
env
napi_value
result
[in] env
: The environment that the API is invoked under.
[out] result
napi_value
representing JavaScript
null
object.
Returns
napi_ok
if the API succeeded.
This API returns the
null
object.
napi_get_undefined
Added in: v8.0.0
N-API Version:
napi_status
napi_get_undefined
napi_env
env
napi_value
result
[in] env
: The environment that the API is invoked under.
[out] result
napi_value
representing JavaScript Undefined value.
Returns
napi_ok
if the API succeeded.
This API returns the Undefined object.
Working with JavaScript values and abstract operations
Node-API exposes a set of APIs to perform some abstract operations on JavaScript
values.
These APIs support doing one of the following:
Coerce JavaScript values to specific JavaScript types (such as
number
or
string
).
Check the type of a JavaScript value.
Check for equality between two JavaScript values.
napi_coerce_to_bool
Added in: v8.0.0
N-API Version:
napi_status
napi_coerce_to_bool
napi_env
env
napi_value
value
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to coerce.
[out] result
napi_value
representing the coerced JavaScript
Boolean
Returns
napi_ok
if the API succeeded.
This API implements the abstract operation
ToBoolean()
as defined in
Section ToBoolean
of the ECMAScript Language Specification.
napi_coerce_to_number
Added in: v8.0.0
N-API Version:
napi_status
napi_coerce_to_number
napi_env
env
napi_value
value
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to coerce.
[out] result
napi_value
representing the coerced JavaScript
number
Returns
napi_ok
if the API succeeded.
This API implements the abstract operation
ToNumber()
as defined in
Section ToNumber
of the ECMAScript Language Specification.
This function potentially runs JS code if the passed-in value is an
object.
napi_coerce_to_object
Added in: v8.0.0
N-API Version:
napi_status
napi_coerce_to_object
napi_env
env
napi_value
value
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to coerce.
[out] result
napi_value
representing the coerced JavaScript
Object
Returns
napi_ok
if the API succeeded.
This API implements the abstract operation
ToObject()
as defined in
Section ToObject
of the ECMAScript Language Specification.
napi_coerce_to_string
Added in: v8.0.0
N-API Version:
napi_status
napi_coerce_to_string
napi_env
env
napi_value
value
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to coerce.
[out] result
napi_value
representing the coerced JavaScript
string
Returns
napi_ok
if the API succeeded.
This API implements the abstract operation
ToString()
as defined in
Section ToString
of the ECMAScript Language Specification.
This function potentially runs JS code if the passed-in value is an
object.
napi_typeof
Added in: v8.0.0
N-API Version:
napi_status
napi_typeof
napi_env
env
napi_value
value
napi_valuetype
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value whose type to query.
[out] result
: The type of the JavaScript value.
Returns
napi_ok
if the API succeeded.
napi_invalid_arg
if the type of
value
is not a known ECMAScript type and
value
is not an External value.
This API represents behavior similar to invoking the
typeof
Operator on
the object as defined in
Section typeof operator
of the ECMAScript Language
Specification. However, there are some differences:
It has support for detecting an External value.
It detects
null
as a separate type, while ECMAScript
typeof
would detect
object
If
value
has a type that is invalid, an error is returned.
napi_instanceof
Added in: v8.0.0
N-API Version:
napi_status
napi_instanceof
napi_env
env
napi_value
object
napi_value
constructor
bool
result
[in] env
: The environment that the API is invoked under.
[in] object
: The JavaScript value to check.
[in] constructor
: The JavaScript function object of the constructor function
to check against.
[out] result
: Boolean that is set to true if
object instanceof constructor
is true.
Returns
napi_ok
if the API succeeded.
This API represents invoking the
instanceof
Operator on the object as
defined in
Section instanceof operator
of the ECMAScript Language Specification.
napi_is_array
Added in: v8.0.0
N-API Version:
napi_status
napi_is_array
napi_env
env
napi_value
value
bool
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to check.
[out] result
: Whether the given object is an array.
Returns
napi_ok
if the API succeeded.
This API represents invoking the
IsArray
operation on the object
as defined in
Section IsArray
of the ECMAScript Language Specification.
napi_is_arraybuffer
Added in: v8.0.0
N-API Version:
napi_status
napi_is_arraybuffer
napi_env
env
napi_value
value
bool
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to check.
[out] result
: Whether the given object is an
ArrayBuffer
Returns
napi_ok
if the API succeeded.
This API checks if the
Object
passed in is an array buffer.
napi_is_buffer
Added in: v8.0.0
N-API Version:
napi_status
napi_is_buffer
napi_env
env
napi_value
value
bool
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to check.
[out] result
: Whether the given
napi_value
represents a
node::Buffer
or
Uint8Array
object.
Returns
napi_ok
if the API succeeded.
This API checks if the
Object
passed in is a buffer or Uint8Array.
napi_is_typedarray
should be preferred if the caller needs to check if the
value is a Uint8Array.
napi_is_date
Added in: v11.11.0, v10.17.0
N-API Version:
napi_status
napi_is_date
napi_env
env
napi_value
value
bool
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to check.
[out] result
: Whether the given
napi_value
represents a JavaScript
Date
object.
Returns
napi_ok
if the API succeeded.
This API checks if the
Object
passed in is a date.
napi_is_error
Added in: v8.0.0
N-API Version:
napi_status
napi_is_error
napi_env
env
napi_value
value
bool
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to check.
[out] result
: Whether the given
napi_value
represents an
Error
object.
Returns
napi_ok
if the API succeeded.
This API checks if the
Object
passed in is an
Error
napi_is_typedarray
Added in: v8.0.0
N-API Version:
napi_status
napi_is_typedarray
napi_env
env
napi_value
value
bool
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to check.
[out] result
: Whether the given
napi_value
represents a
TypedArray
Returns
napi_ok
if the API succeeded.
This API checks if the
Object
passed in is a typed array.
napi_is_dataview
Added in: v8.3.0
N-API Version:
napi_status
napi_is_dataview
napi_env
env
napi_value
value
bool
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to check.
[out] result
: Whether the given
napi_value
represents a
DataView
Returns
napi_ok
if the API succeeded.
This API checks if the
Object
passed in is a
DataView
napi_strict_equals
Added in: v8.0.0
N-API Version:
napi_status
napi_strict_equals
napi_env
env
napi_value
lhs
napi_value
rhs
bool
result
[in] env
: The environment that the API is invoked under.
[in] lhs
: The JavaScript value to check.
[in] rhs
: The JavaScript value to check against.
[out] result
: Whether the two
napi_value
objects are equal.
Returns
napi_ok
if the API succeeded.
This API represents the invocation of the Strict Equality algorithm as
defined in
Section IsStrctEqual
of the ECMAScript Language Specification.
napi_detach_arraybuffer
Added in: v13.0.0, v12.16.0, v10.22.0
N-API Version:
napi_status
napi_detach_arraybuffer
napi_env
env
napi_value
arraybuffer
[in] env
: The environment that the API is invoked under.
[in] arraybuffer
: The JavaScript
ArrayBuffer
to be detached.
Returns
napi_ok
if the API succeeded. If a non-detachable
ArrayBuffer
is
passed in it returns
napi_detachable_arraybuffer_expected
Generally, an
ArrayBuffer
is non-detachable if it has been detached before.
The engine may impose additional conditions on whether an
ArrayBuffer
is
detachable. For example, V8 requires that the
ArrayBuffer
be external,
that is, created with
napi_create_external_arraybuffer
This API represents the invocation of the
ArrayBuffer
detach operation as
defined in
Section detachArrayBuffer
of the ECMAScript Language Specification.
napi_is_detached_arraybuffer
Added in: v13.3.0, v12.16.0, v10.22.0
N-API Version:
napi_status
napi_is_detached_arraybuffer
napi_env
env
napi_value
arraybuffer
bool
result
[in] env
: The environment that the API is invoked under.
[in] arraybuffer
: The JavaScript
ArrayBuffer
to be checked.
[out] result
: Whether the
arraybuffer
is detached.
Returns
napi_ok
if the API succeeded.
The
ArrayBuffer
is considered detached if its internal data is
null
This API represents the invocation of the
ArrayBuffer
IsDetachedBuffer
operation as defined in
Section isDetachedBuffer
of the ECMAScript Language
Specification.
node_api_is_sharedarraybuffer
Added in: v24.9.0
Stability: 1 - Experimental
napi_status
node_api_is_sharedarraybuffer
napi_env
env
napi_value
value
bool
result
[in] env
: The environment that the API is invoked under.
[in] value
: The JavaScript value to check.
[out] result
: Whether the given
napi_value
represents a
SharedArrayBuffer
Returns
napi_ok
if the API succeeded.
This API checks if the Object passed in is a
SharedArrayBuffer
node_api_create_sharedarraybuffer
Added in: v24.9.0
Stability: 1 - Experimental
napi_status
node_api_create_sharedarraybuffer
napi_env
env
size_t
byte_length
void
**
data
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] byte_length
: The length in bytes of the shared array buffer to create.
[out] data
: Pointer to the underlying byte buffer of the
SharedArrayBuffer
data
can optionally be ignored by passing
NULL
[out] result
: A
napi_value
representing a JavaScript
SharedArrayBuffer
Returns
napi_ok
if the API succeeded.
This API returns a Node-API value corresponding to a JavaScript
SharedArrayBuffer
SharedArrayBuffer
s are used to represent fixed-length binary data buffers that
can be shared across multiple workers.
The
SharedArrayBuffer
allocated will have an underlying byte buffer whose size is
determined by the
byte_length
parameter that's passed in.
The underlying buffer is optionally returned back to the caller in case the
caller wants to directly manipulate the buffer. This buffer can only be
written to directly from native code. To write to this buffer from JavaScript,
a typed array or
DataView
object would need to be created.
JavaScript
SharedArrayBuffer
objects are described in
Section SharedArrayBuffer objects
of the ECMAScript Language Specification.
Working with JavaScript properties
Node-API exposes a set of APIs to get and set properties on JavaScript
objects.
Properties in JavaScript are represented as a tuple of a key and a value.
Fundamentally, all property keys in Node-API can be represented in one of the
following forms:
Named: a simple UTF8-encoded string
Integer-Indexed: an index value represented by
uint32_t
JavaScript value: these are represented in Node-API by
napi_value
. This can
be a
napi_value
representing a
string
number
, or
symbol
Node-API values are represented by the type
napi_value
Any Node-API call that requires a JavaScript value takes in a
napi_value
However, it's the caller's responsibility to make sure that the
napi_value
in question is of the JavaScript type expected by the API.
The APIs documented in this section provide a simple interface to
get and set properties on arbitrary JavaScript objects represented by
napi_value
For instance, consider the following JavaScript code snippet:
const
obj
{};
obj
myProp
123
The equivalent can be done using Node-API values with the following snippet:
napi_status status
napi_generic_failure
// const obj = {}
napi_value obj
value
status
napi_create_object
env
obj
);
if
status
!=
napi_ok
return
status
// Create a napi_value for 123
status
napi_create_int32
env
123
value
);
if
status
!=
napi_ok
return
status
// obj.myProp = 123
status
napi_set_named_property
env
obj
"myProp"
value
);
if
status
!=
napi_ok
return
status
Indexed properties can be set in a similar manner. Consider the following
JavaScript snippet:
const
arr
[]
arr[
123
'hello'
The equivalent can be done using Node-API values with the following snippet:
napi_status status
napi_generic_failure
// const arr = [];
napi_value arr
value
status
napi_create_array
env
arr
);
if
status
!=
napi_ok
return
status
// Create a napi_value for 'hello'
status
napi_create_string_utf8
env
"hello"
NAPI_AUTO_LENGTH
value
);
if
status
!=
napi_ok
return
status
// arr[123] = 'hello';
status
napi_set_element
env
arr
123
value
);
if
status
!=
napi_ok
return
status
Properties can be retrieved using the APIs described in this section.
Consider the following JavaScript snippet:
const
arr
[]
const
value
arr[
123
The following is the approximate equivalent of the Node-API counterpart:
napi_status status
napi_generic_failure
// const arr = []
napi_value arr
value
status
napi_create_array
env
arr
);
if
status
!=
napi_ok
return
status
// const value = arr[123]
status
napi_get_element
env
arr
123
value
);
if
status
!=
napi_ok
return
status
Finally, multiple properties can also be defined on an object for performance
reasons. Consider the following JavaScript:
const
obj
{};
Object
defineProperties
(obj
'foo'
value
123
writable
true
configurable
true
enumerable
true
},
'bar'
value
456
writable
true
configurable
true
enumerable
true
},
The following is the approximate equivalent of the Node-API counterpart:
napi_status status
napi_status_generic_failure
// const obj = {};
napi_value obj
status
napi_create_object
env
obj
);
if
status
!=
napi_ok
return
status
// Create napi_values for 123 and 456
napi_value fooValue
barValue
status
napi_create_int32
env
123
fooValue
);
if
status
!=
napi_ok
return
status
status
napi_create_int32
env
456
barValue
);
if
status
!=
napi_ok
return
status
// Set the properties
napi_property_descriptor descriptors
[]
"foo"
NULL
NULL
NULL
NULL
fooValue
napi_writable
napi_configurable
NULL
},
"bar"
NULL
NULL
NULL
NULL
barValue
napi_writable
napi_configurable
NULL
status
napi_define_properties
env
obj
sizeof
descriptors
sizeof
descriptors
]),
descriptors
);
if
status
!=
napi_ok
return
status
Structures
napi_property_attributes
History
Version
Changes
v14.12.0
added
napi_default_method
and
napi_default_property
typedef
enum
napi_default
napi_writable
<<
napi_enumerable
<<
napi_configurable
<<
// Used with napi_define_class to distinguish static properties
// from instance properties. Ignored by napi_define_properties.
napi_static
<<
10
// Default for class methods.
napi_default_method
napi_writable
napi_configurable
// Default for object properties, like in JS obj[prop].
napi_default_jsproperty
napi_writable
napi_enumerable
napi_configurable
napi_property_attributes
napi_property_attributes
are bit flags used to control the behavior of
properties set on a JavaScript object. Other than
napi_static
they
correspond to the attributes listed in
Section property attributes
of the
ECMAScript Language Specification
They can be one or more of the following bit flags:
napi_default
: No explicit attributes are set on the property. By default, a
property is read only, not enumerable and not configurable.
napi_writable
: The property is writable.
napi_enumerable
: The property is enumerable.
napi_configurable
: The property is configurable as defined in
Section property attributes
of the
ECMAScript Language Specification
napi_static
: The property will be defined as a static property on a class as
opposed to an instance property, which is the default. This is used only by
napi_define_class
. It is ignored by
napi_define_properties
napi_default_method
: Like a method in a JS class, the property is
configurable and writeable, but not enumerable.
napi_default_jsproperty
: Like a property set via assignment in JavaScript,
the property is writable, enumerable, and configurable.
napi_property_descriptor
typedef
struct
// One of utf8name or name should be NULL.
const
char
utf8name
napi_value name
napi_callback method
napi_callback getter
napi_callback setter
napi_value value
napi_property_attributes attributes
void
data
napi_property_descriptor
utf8name
: Optional string describing the key for the property,
encoded as UTF8. One of
utf8name
or
name
must be provided for the
property.
name
: Optional
napi_value
that points to a JavaScript string or symbol
to be used as the key for the property. One of
utf8name
or
name
must
be provided for the property.
value
: The value that's retrieved by a get access of the property if the
property is a data property. If this is passed in, set
getter
setter
method
and
data
to
NULL
(since these members won't be used).
getter
: A function to call when a get access of the property is performed.
If this is passed in, set
value
and
method
to
NULL
(since these members
won't be used). The given function is called implicitly by the runtime when
the property is accessed from JavaScript code (or if a get on the property is
performed using a Node-API call).
napi_callback
provides more details.
setter
: A function to call when a set access of the property is performed.
If this is passed in, set
value
and
method
to
NULL
(since these members
won't be used). The given function is called implicitly by the runtime when
the property is set from JavaScript code (or if a set on the property is
performed using a Node-API call).
napi_callback
provides more details.
method
: Set this to make the property descriptor object's
value
property to be a JavaScript function represented by
method
. If this is
passed in, set
value
getter
and
setter
to
NULL
(since these members
won't be used).
napi_callback
provides more details.
attributes
: The attributes associated with the particular property. See
napi_property_attributes
data
: The callback data passed into
method
getter
and
setter
if this
function is invoked.
Functions
napi_get_property_names
Added in: v8.0.0
N-API Version:
napi_status
napi_get_property_names
napi_env
env
napi_value
object
napi_value
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object from which to retrieve the properties.
[out] result
: A
napi_value
representing an array of JavaScript values
that represent the property names of the object. The API can be used to
iterate over
result
using
napi_get_array_length
and
napi_get_element
Returns
napi_ok
if the API succeeded.
This API returns the names of the enumerable properties of
object
as an array
of strings. The properties of
object
whose key is a symbol will not be
included.
napi_get_all_property_names
Added in: v13.7.0, v12.17.0, v10.20.0
N-API Version:
napi_get_all_property_names
napi_env
env
napi_value
object
napi_key_collection_mode
key_mode
napi_key_filter
key_filter
napi_key_conversion
key_conversion
napi_value
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object from which to retrieve the properties.
[in] key_mode
: Whether to retrieve prototype properties as well.
[in] key_filter
: Which properties to retrieve
(enumerable/readable/writable).
[in] key_conversion
: Whether to convert numbered property keys to strings.
[out] result
: A
napi_value
representing an array of JavaScript values
that represent the property names of the object.
napi_get_array_length
and
napi_get_element
can be used to iterate over
result
Returns
napi_ok
if the API succeeded.
This API returns an array containing the names of the available properties
of this object.
napi_set_property
Added in: v8.0.0
N-API Version:
napi_status
napi_set_property
napi_env
env
napi_value
object
napi_value
key
napi_value
value
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object on which to set the property.
[in] key
: The name of the property to set.
[in] value
: The property value.
Returns
napi_ok
if the API succeeded.
This API set a property on the
Object
passed in.
napi_get_property
Added in: v8.0.0
N-API Version:
napi_status
napi_get_property
napi_env
env
napi_value
object
napi_value
key
napi_value
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object from which to retrieve the property.
[in] key
: The name of the property to retrieve.
[out] result
: The value of the property.
Returns
napi_ok
if the API succeeded.
This API gets the requested property from the
Object
passed in.
napi_has_property
Added in: v8.0.0
N-API Version:
napi_status
napi_has_property
napi_env
env
napi_value
object
napi_value
key
bool
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object to query.
[in] key
: The name of the property whose existence to check.
[out] result
: Whether the property exists on the object or not.
Returns
napi_ok
if the API succeeded.
This API checks if the
Object
passed in has the named property.
napi_delete_property
Added in: v8.2.0
N-API Version:
napi_status
napi_delete_property
napi_env
env
napi_value
object
napi_value
key
bool
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object to query.
[in] key
: The name of the property to delete.
[out] result
: Whether the property deletion succeeded or not.
result
can
optionally be ignored by passing
NULL
Returns
napi_ok
if the API succeeded.
This API attempts to delete the
key
own property from
object
napi_has_own_property
Added in: v8.2.0
N-API Version:
napi_status
napi_has_own_property
napi_env
env
napi_value
object
napi_value
key
bool
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object to query.
[in] key
: The name of the own property whose existence to check.
[out] result
: Whether the own property exists on the object or not.
Returns
napi_ok
if the API succeeded.
This API checks if the
Object
passed in has the named own property.
key
must
be a
string
or a
symbol
, or an error will be thrown. Node-API will not
perform any conversion between data types.
napi_set_named_property
Added in: v8.0.0
N-API Version:
napi_status
napi_set_named_property
napi_env
env
napi_value
object
const
char
utf8Name
napi_value
value
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object on which to set the property.
[in] utf8Name
: The name of the property to set.
[in] value
: The property value.
Returns
napi_ok
if the API succeeded.
This method is equivalent to calling
napi_set_property
with a
napi_value
created from the string passed in as
utf8Name
napi_get_named_property
Added in: v8.0.0
N-API Version:
napi_status
napi_get_named_property
napi_env
env
napi_value
object
const
char
utf8Name
napi_value
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object from which to retrieve the property.
[in] utf8Name
: The name of the property to get.
[out] result
: The value of the property.
Returns
napi_ok
if the API succeeded.
This method is equivalent to calling
napi_get_property
with a
napi_value
created from the string passed in as
utf8Name
napi_has_named_property
Added in: v8.0.0
N-API Version:
napi_status
napi_has_named_property
napi_env
env
napi_value
object
const
char
utf8Name
bool
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object to query.
[in] utf8Name
: The name of the property whose existence to check.
[out] result
: Whether the property exists on the object or not.
Returns
napi_ok
if the API succeeded.
This method is equivalent to calling
napi_has_property
with a
napi_value
created from the string passed in as
utf8Name
napi_set_element
Added in: v8.0.0
N-API Version:
napi_status
napi_set_element
napi_env
env
napi_value
object
uint32_t
index
napi_value
value
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object from which to set the properties.
[in] index
: The index of the property to set.
[in] value
: The property value.
Returns
napi_ok
if the API succeeded.
This API sets an element on the
Object
passed in.
napi_get_element
Added in: v8.0.0
N-API Version:
napi_status
napi_get_element
napi_env
env
napi_value
object
uint32_t
index
napi_value
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object from which to retrieve the property.
[in] index
: The index of the property to get.
[out] result
: The value of the property.
Returns
napi_ok
if the API succeeded.
This API gets the element at the requested index.
napi_has_element
Added in: v8.0.0
N-API Version:
napi_status
napi_has_element
napi_env
env
napi_value
object
uint32_t
index
bool
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object to query.
[in] index
: The index of the property whose existence to check.
[out] result
: Whether the property exists on the object or not.
Returns
napi_ok
if the API succeeded.
This API returns if the
Object
passed in has an element at the
requested index.
napi_delete_element
Added in: v8.2.0
N-API Version:
napi_status
napi_delete_element
napi_env
env
napi_value
object
uint32_t
index
bool
result
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object to query.
[in] index
: The index of the property to delete.
[out] result
: Whether the element deletion succeeded or not.
result
can
optionally be ignored by passing
NULL
Returns
napi_ok
if the API succeeded.
This API attempts to delete the specified
index
from
object
napi_define_properties
Added in: v8.0.0
N-API Version:
napi_status
napi_define_properties
napi_env
env
napi_value
object
size_t
property_count
const
napi_property_descriptor
properties
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object from which to retrieve the properties.
[in] property_count
: The number of elements in the
properties
array.
[in] properties
: The array of property descriptors.
Returns
napi_ok
if the API succeeded.
This method allows the efficient definition of multiple properties on a given
object. The properties are defined using property descriptors (see
napi_property_descriptor
). Given an array of such property descriptors,
this API will set the properties on the object one at a time, as defined by
DefineOwnProperty()
(described in
Section DefineOwnProperty
of the ECMA-262
specification).
napi_object_freeze
Added in: v14.14.0, v12.20.0
N-API Version:
napi_status
napi_object_freeze
napi_env
env
napi_value
object
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object to freeze.
Returns
napi_ok
if the API succeeded.
This method freezes a given object. This prevents new properties from
being added to it, existing properties from being removed, prevents
changing the enumerability, configurability, or writability of existing
properties, and prevents the values of existing properties from being changed.
It also prevents the object's prototype from being changed. This is described
in
Section 19.1.2.6
of the
ECMA-262 specification.
napi_object_seal
Added in: v14.14.0, v12.20.0
N-API Version:
napi_status
napi_object_seal
napi_env
env
napi_value
object
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object to seal.
Returns
napi_ok
if the API succeeded.
This method seals a given object. This prevents new properties from being
added to it, as well as marking all existing properties as non-configurable.
This is described in
Section 19.1.2.20
of the ECMA-262 specification.
node_api_set_prototype
Added in: v25.4.0
Stability: 1 - Experimental
napi_status
node_api_set_prototype
napi_env
env
napi_value
object
napi_value
value
);
[in] env
: The environment that the Node-API call is invoked under.
[in] object
: The object on which to set the prototype.
[in] value
: The prototype value.
Returns
napi_ok
if the API succeeded.
This API sets the prototype of the
Object
passed in.
Working with JavaScript functions
Node-API provides a set of APIs that allow JavaScript code to
call back into native code. Node-APIs that support calling back
into native code take in a callback functions represented by
the
napi_callback
type. When the JavaScript VM calls back to
native code, the
napi_callback
function provided is invoked. The APIs
documented in this section allow the callback function to do the
following:
Get information about the context in which the callback was invoked.
Get the arguments passed into the callback.
Return a
napi_value
back from the callback.
Additionally, Node-API provides a set of functions which allow calling
JavaScript functions from native code. One can either call a function
like a regular JavaScript function call, or as a constructor
function.
Any non-
NULL
data which is passed to this API via the
data
field of the
napi_property_descriptor
items can be associated with
object
and freed
whenever
object
is garbage-collected by passing both
object
and the data to
napi_add_finalizer
napi_call_function
Added in: v8.0.0
N-API Version:
NAPI_EXTERN napi_status
napi_call_function
napi_env
env
napi_value
recv
napi_value
func
size_t
argc
const
napi_value
argv
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] recv
: The
this
value passed to the called function.
[in] func
napi_value
representing the JavaScript function to be invoked.
[in] argc
: The count of elements in the
argv
array.
[in] argv
: Array of
napi_values
representing JavaScript values passed in
as arguments to the function.
[out] result
napi_value
representing the JavaScript object returned.
Returns
napi_ok
if the API succeeded.
This method allows a JavaScript function object to be called from a native
add-on. This is the primary mechanism of calling back
from
the add-on's
native code
into
JavaScript. For the special case of calling into JavaScript
after an async operation, see
napi_make_callback
A sample use case might look as follows. Consider the following JavaScript
snippet:
function
AddTwo
num
return
num
global
AddTwo
AddTwo
Then, the above function can be invoked from a native add-on using the
following code:
// Get the function named "AddTwo" on the global object
napi_value global
add_two
arg
napi_status status
napi_get_global
env
global
);
if
status
!=
napi_ok
return
status
napi_get_named_property
env
global
"AddTwo"
add_two
);
if
status
!=
napi_ok
return
// const arg = 1337
status
napi_create_int32
env
1337
arg
);
if
status
!=
napi_ok
return
napi_value
argv
arg
size_t
argc
// AddTwo(arg);
napi_value return_val
status
napi_call_function
env
global
add_two
argc
argv
return_val
);
if
status
!=
napi_ok
return
// Convert the result back to a native type
int32_t
result
status
napi_get_value_int32
env
return_val
result
);
if
status
!=
napi_ok
return
napi_create_function
Added in: v8.0.0
N-API Version:
napi_status
napi_create_function
napi_env
env
const
char
utf8name
size_t
length
napi_callback
cb
void
data
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] utf8Name
: Optional name of the function encoded as UTF8. This is
visible within JavaScript as the new function object's
name
property.
[in] length
: The length of the
utf8name
in bytes, or
NAPI_AUTO_LENGTH
if
it is null-terminated.
[in] cb
: The native function which should be called when this function
object is invoked.
napi_callback
provides more details.
[in] data
: User-provided data context. This will be passed back into the
function when invoked later.
[out] result
napi_value
representing the JavaScript function object for
the newly created function.
Returns
napi_ok
if the API succeeded.
This API allows an add-on author to create a function object in native code.
This is the primary mechanism to allow calling
into
the add-on's native code
from
JavaScript.
The newly created function is not automatically visible from script after this
call. Instead, a property must be explicitly set on any object that is visible
to JavaScript, in order for the function to be accessible from script.
In order to expose a function as part of the
add-on's module exports, set the newly created function on the exports
object. A sample module might look as follows:
napi_value
SayHello
napi_env
env
napi_callback_info
info
printf
"Hello
\n
);
return
NULL
napi_value
Init
napi_env
env
napi_value
exports
napi_status status
napi_value fn
status
napi_create_function
env
NULL
SayHello
NULL
fn
);
if
status
!=
napi_ok
return
NULL
status
napi_set_named_property
env
exports
"sayHello"
fn
);
if
status
!=
napi_ok
return
NULL
return
exports
NAPI_MODULE
NODE_GYP_MODULE_NAME
Init
Given the above code, the add-on can be used from JavaScript as follows:
const
myaddon
require
'./addon'
myaddon
sayHello
()
The string passed to
require()
is the name of the target in
binding.gyp
responsible for creating the
.node
file.
Any non-
NULL
data which is passed to this API via the
data
parameter can
be associated with the resulting JavaScript function (which is returned in the
result
parameter) and freed whenever the function is garbage-collected by
passing both the JavaScript function and the data to
napi_add_finalizer
JavaScript
Function
s are described in
Section Function objects
of the ECMAScript
Language Specification.
napi_get_cb_info
Added in: v8.0.0
N-API Version:
napi_status
napi_get_cb_info
napi_env
env
napi_callback_info
cbinfo
size_t
argc
napi_value
argv
napi_value
thisArg
void
**
data
[in] env
: The environment that the API is invoked under.
[in] cbinfo
: The callback info passed into the callback function.
[in-out] argc
: Specifies the length of the provided
argv
array and
receives the actual count of arguments.
argc
can
optionally be ignored by passing
NULL
[out] argv
: C array of
napi_value
s to which the arguments will be
copied. If there are more arguments than the provided count, only the
requested number of arguments are copied. If there are fewer arguments
provided than claimed, the rest of
argv
is filled with
napi_value
values
that represent
undefined
argv
can optionally be ignored by
passing
NULL
[out] thisArg
: Receives the JavaScript
this
argument for the call.
thisArg
can optionally be ignored by passing
NULL
[out] data
: Receives the data pointer for the callback.
data
can
optionally be ignored by passing
NULL
Returns
napi_ok
if the API succeeded.
This method is used within a callback function to retrieve details about the
call like the arguments and the
this
pointer from a given callback info.
napi_get_new_target
Added in: v8.6.0
N-API Version:
napi_status
napi_get_new_target
napi_env
env
napi_callback_info
cbinfo
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] cbinfo
: The callback info passed into the callback function.
[out] result
: The
new.target
of the constructor call.
Returns
napi_ok
if the API succeeded.
This API returns the
new.target
of the constructor call. If the current
callback is not a constructor call, the result is
NULL
napi_new_instance
Added in: v8.0.0
N-API Version:
napi_status
napi_new_instance
napi_env
env
napi_value
cons
size_t
argc
napi_value
argv
napi_value
result
[in] env
: The environment that the API is invoked under.
[in] cons
napi_value
representing the JavaScript function to be invoked
as a constructor.
[in] argc
: The count of elements in the
argv
array.
[in] argv
: Array of JavaScript values as
napi_value
representing the
arguments to the constructor. If
argc
is zero this parameter may be
omitted by passing in
NULL
[out] result
napi_value
representing the JavaScript object returned,
which in this case is the constructed object.
This method is used to instantiate a new JavaScript value using a given
napi_value
that represents the constructor for the object. For example,
consider the following snippet:
function
MyObject
param
this
param
param
const
arg
'hello'
const
value
new
MyObject
(arg)
The following can be approximated in Node-API using the following snippet:
// Get the constructor function MyObject
napi_value global
constructor
arg
value
napi_status status
napi_get_global
env
global
);
if
status
!=
napi_ok
return
status
napi_get_named_property
env
global
"MyObject"
constructor
);
if
status
!=
napi_ok
return
// const arg = "hello"
status
napi_create_string_utf8
env
"hello"
NAPI_AUTO_LENGTH
arg
);
if
status
!=
napi_ok
return
napi_value
argv
arg
size_t
argc
// const value = new MyObject(arg)
status
napi_new_instance
env
constructor
argc
argv
value
);
Returns
napi_ok
if the API succeeded.
Object wrap
Node-API offers a way to "wrap" C++ classes and instances so that the class
constructor and methods can be called from JavaScript.
The
napi_define_class
API defines a JavaScript class with constructor,
static properties and methods, and instance properties and methods that
correspond to the C++ class.
When JavaScript code invokes the constructor, the constructor callback
uses
napi_wrap
to wrap a new C++ instance in a JavaScript object,
then returns the wrapper object.
When JavaScript code invokes a method or property accessor on the class,
the corresponding
napi_callback
C++ function is invoked. For an instance
callback,
napi_unwrap
obtains the C++ instance that is the target of
the call.
For wrapped objects it may be difficult to distinguish between a function
called on a class prototype and a function called on an instance of a class.
A common pattern used to address this problem is to save a persistent
reference to the class constructor for later
instanceof
checks.
napi_value MyClass_constructor
NULL
status
napi_get_reference_value
env
MyClass::es_constructor
MyClass_constructor
);
assert
napi_ok
==
status
);
bool
is_instance
false
status
napi_instanceof
env
es_this
MyClass_constructor
is_instance
);
assert
napi_ok
==
status
);
if
is_instance
// napi_unwrap() ...
else
// otherwise...
The reference must be freed once it is no longer needed.
There are occasions where
napi_instanceof()
is insufficient for ensuring that
a JavaScript object is a wrapper for a certain native type. This is the case
especially when wrapped JavaScript objects are passed back into the addon via
static methods rather than as the
this
value of prototype methods. In such
cases there is a chance that they may be unwrapped incorrectly.
const
myAddon
require
'./build/Release/my_addon.node'
// `openDatabase()` returns a JavaScript object that wraps a native database
// handle.
const
dbHandle
myAddon
openDatabase
()
// `query()` returns a JavaScript object that wraps a native query handle.
const
queryHandle
myAddon
query
(dbHandle
'Gimme ALL the things!'
// There is an accidental error in the line below. The first parameter to
// `myAddon.queryHasRecords()` should be the database handle (`dbHandle`), not
// the query handle (`query`), so the correct condition for the while-loop
// should be
//
// myAddon.queryHasRecords(dbHandle, queryHandle)
//
while
(myAddon
queryHasRecords
(queryHandle
dbHandle))
// retrieve records
In the above example
myAddon.queryHasRecords()
is a method that accepts two
arguments. The first is a database handle and the second is a query handle.
Internally, it unwraps the first argument and casts the resulting pointer to a
native database handle. It then unwraps the second argument and casts the
resulting pointer to a query handle. If the arguments are passed in the wrong
order, the casts will work, however, there is a good chance that the underlying
database operation will fail, or will even cause an invalid memory access.
To ensure that the pointer retrieved from the first argument is indeed a pointer
to a database handle and, similarly, that the pointer retrieved from the second
argument is indeed a pointer to a query handle, the implementation of
queryHasRecords()
has to perform a type validation. Retaining the JavaScript
class constructor from which the database handle was instantiated and the
constructor from which the query handle was instantiated in
napi_ref
s can
help, because
napi_instanceof()
can then be used to ensure that the instances
passed into
queryHashRecords()
are indeed of the correct type.
Unfortunately,
napi_instanceof()
does not protect against prototype
manipulation. For example, the prototype of the database handle instance can be
set to the prototype of the constructor for query handle instances. In this
case, the database handle instance can appear as a query handle instance, and it
will pass the
napi_instanceof()
test for a query handle instance, while still
containing a pointer to a database handle.
To this end, Node-API provides type-tagging capabilities.
A type tag is a 128-bit integer unique to the addon. Node-API provides the
napi_type_tag
structure for storing a type tag. When such a value is passed
along with a JavaScript object or
external
stored in a
napi_value
to
napi_type_tag_object()
, the JavaScript object will be "marked" with the
type tag. The "mark" is invisible on the JavaScript side. When a JavaScript
object arrives into a native binding,
napi_check_object_type_tag()
can be used
along with the original type tag to determine whether the JavaScript object was
previously "marked" with the type tag. This creates a type-checking capability
of a higher fidelity than
napi_instanceof()
can provide, because such type-
tagging survives prototype manipulation and addon unloading/reloading.
Continuing the above example, the following skeleton addon implementation
illustrates the use of
napi_type_tag_object()
and
napi_check_object_type_tag()
// This value is the type tag for a database handle. The command
//
// uuidgen | sed -r -e 's/-//g' -e 's/(.{16})(.*)/0x\1, 0x\2/'
//
// can be used to obtain the two values with which to initialize the structure.
static
const
napi_type_tag DatabaseHandleTypeTag
0x
1edf75a38336451d
0x
a5ed9ce2e4c00c38
};
// This value is the type tag for a query handle.
static
const
napi_type_tag QueryHandleTypeTag
0x
9c73317f9fad44a3
0x
93c3920bf3b0ad6a
};
static
napi_value
openDatabase
napi_env
env
napi_callback_info
info
napi_status status
napi_value result
// Perform the underlying action which results in a database handle.
DatabaseHandle
dbHandle
open_database
();
// Create a new, empty JS object.
status
napi_create_object
env
result
);
if
status
!=
napi_ok
return
NULL
// Tag the object to indicate that it holds a pointer to a `DatabaseHandle`.
status
napi_type_tag_object
env
result
DatabaseHandleTypeTag
);
if
status
!=
napi_ok
return
NULL
// Store the pointer to the `DatabaseHandle` structure inside the JS object.
status
napi_wrap
env
result
dbHandle
NULL
NULL
NULL
);
if
status
!=
napi_ok
return
NULL
return
result
// Later when we receive a JavaScript object purporting to be a database handle
// we can use `napi_check_object_type_tag()` to ensure that it is indeed such a
// handle.
static
napi_value
query
napi_env
env
napi_callback_info
info
napi_status status
size_t
argc
napi_value argv
];
bool
is_db_handle
status
napi_get_cb_info
env
info
argc
argv
NULL
NULL
);
if
status
!=
napi_ok
return
NULL
// Check that the object passed as the first parameter has the previously
// applied tag.
status
napi_check_object_type_tag
env
argv
],
DatabaseHandleTypeTag
is_db_handle
);
if
status
!=
napi_ok
return
NULL
// Throw a `TypeError` if it doesn't.
if
is_db_handle
// Throw a TypeError.
return
NULL
napi_define_class
Added in: v8.0.0
N-API Version:
napi_status
napi_define_class
napi_env
env
const
char
utf8name
size_t
length
napi_callback
constructor
void
data
size_t
property_count
const
napi_property_descriptor
properties
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] utf8name
: Name of the JavaScript constructor function. For clarity,
it is recommended to use the C++ class name when wrapping a C++ class.
[in] length
: The length of the
utf8name
in bytes, or
NAPI_AUTO_LENGTH
if it is null-terminated.
[in] constructor
: Callback function that handles constructing instances
of the class. When wrapping a C++ class, this method must be a static member
with the
napi_callback
signature. A C++ class constructor cannot be
used.
napi_callback
provides more details.
[in] data
: Optional data to be passed to the constructor callback as
the
data
property of the callback info.
[in] property_count
: Number of items in the
properties
array argument.
[in] properties
: Array of property descriptors describing static and
instance data properties, accessors, and methods on the class
See
napi_property_descriptor
[out] result
: A
napi_value
representing the constructor function for
the class.
Returns
napi_ok
if the API succeeded.
Defines a JavaScript class, including:
A JavaScript constructor function that has the class name. When wrapping a
corresponding C++ class, the callback passed via
constructor
can be used to
instantiate a new C++ class instance, which can then be placed inside the
JavaScript object instance being constructed using
napi_wrap
Properties on the constructor function whose implementation can call
corresponding
static
data properties, accessors, and methods of the C++
class (defined by property descriptors with the
napi_static
attribute).
Properties on the constructor function's
prototype
object. When wrapping a
C++ class,
non-static
data properties, accessors, and methods of the C++
class can be called from the static functions given in the property
descriptors without the
napi_static
attribute after retrieving the C++ class
instance placed inside the JavaScript object instance by using
napi_unwrap
When wrapping a C++ class, the C++ constructor callback passed via
constructor
should be a static method on the class that calls the actual class constructor,
then wraps the new C++ instance in a JavaScript object, and returns the wrapper
object. See
napi_wrap
for details.
The JavaScript constructor function returned from
napi_define_class
is
often saved and used later to construct new instances of the class from native
code, and/or to check whether provided values are instances of the class. In
that case, to prevent the function value from being garbage-collected, a
strong persistent reference to it can be created using
napi_create_reference
, ensuring that the reference count is kept >= 1.
Any non-
NULL
data which is passed to this API via the
data
parameter or via
the
data
field of the
napi_property_descriptor
array items can be associated
with the resulting JavaScript constructor (which is returned in the
result
parameter) and freed whenever the class is garbage-collected by passing both
the JavaScript function and the data to
napi_add_finalizer
napi_wrap
Added in: v8.0.0
N-API Version:
napi_status
napi_wrap
napi_env
env
napi_value
js_object
void
native_object
napi_finalize
finalize_cb
void
finalize_hint
napi_ref
result
);
[in] env
: The environment that the API is invoked under.
[in] js_object
: The JavaScript object that will be the wrapper for the
native object.
[in] native_object
: The native instance that will be wrapped in the
JavaScript object.
[in] finalize_cb
: Optional native callback that can be used to free the
native instance when the JavaScript object has been garbage-collected.
napi_finalize
provides more details.
[in] finalize_hint
: Optional contextual hint that is passed to the
finalize callback.
[out] result
: Optional reference to the wrapped object.
Returns
napi_ok
if the API succeeded.
Wraps a native instance in a JavaScript object. The native instance can be
retrieved later using
napi_unwrap()
When JavaScript code invokes a constructor for a class that was defined using
napi_define_class()
, the
napi_callback
for the constructor is invoked.
After constructing an instance of the native class, the callback must then call
napi_wrap()
to wrap the newly constructed instance in the already-created
JavaScript object that is the
this
argument to the constructor callback.
(That
this
object was created from the constructor function's
prototype
so it already has definitions of all the instance properties and methods.)
Typically when wrapping a class instance, a finalize callback should be
provided that simply deletes the native instance that is received as the
data
argument to the finalize callback.
The optional returned reference is initially a weak reference, meaning it
has a reference count of 0. Typically this reference count would be incremented
temporarily during async operations that require the instance to remain valid.
Caution
: The optional returned reference (if obtained) should be deleted via
napi_delete_reference
ONLY in response to the finalize callback
invocation. If it is deleted before then, then the finalize callback may never
be invoked. Therefore, when obtaining a reference a finalize callback is also
required in order to enable correct disposal of the reference.
Finalizer callbacks may be deferred, leaving a window where the object has
been garbage collected (and the weak reference is invalid) but the finalizer
hasn't been called yet. When using
napi_get_reference_value()
on weak
references returned by
napi_wrap()
, you should still handle an empty result.
Calling
napi_wrap()
a second time on an object will return an error. To
associate another native instance with the object, use
napi_remove_wrap()
first.
napi_unwrap
Added in: v8.0.0
N-API Version:
napi_status
napi_unwrap
napi_env
env
napi_value
js_object
void
**
result
);
[in] env
: The environment that the API is invoked under.
[in] js_object
: The object associated with the native instance.
[out] result
: Pointer to the wrapped native instance.
Returns
napi_ok
if the API succeeded.
Retrieves a native instance that was previously wrapped in a JavaScript
object using
napi_wrap()
When JavaScript code invokes a method or property accessor on the class, the
corresponding
napi_callback
is invoked. If the callback is for an instance
method or accessor, then the
this
argument to the callback is the wrapper
object; the wrapped C++ instance that is the target of the call can be obtained
then by calling
napi_unwrap()
on the wrapper object.
napi_remove_wrap
Added in: v8.5.0
N-API Version:
napi_status
napi_remove_wrap
napi_env
env
napi_value
js_object
void
**
result
);
[in] env
: The environment that the API is invoked under.
[in] js_object
: The object associated with the native instance.
[out] result
: Pointer to the wrapped native instance.
Returns
napi_ok
if the API succeeded.
Retrieves a native instance that was previously wrapped in the JavaScript
object
js_object
using
napi_wrap()
and removes the wrapping. If a finalize
callback was associated with the wrapping, it will no longer be called when the
JavaScript object becomes garbage-collected.
napi_type_tag_object
Added in: v14.8.0, v12.19.0
N-API Version:
napi_status
napi_type_tag_object
napi_env
env
napi_value
js_object
const
napi_type_tag
type_tag
);
[in] env
: The environment that the API is invoked under.
[in] js_object
: The JavaScript object or
external
to be marked.
[in] type_tag
: The tag with which the object is to be marked.
Returns
napi_ok
if the API succeeded.
Associates the value of the
type_tag
pointer with the JavaScript object or
external
napi_check_object_type_tag()
can then be used to compare the tag
that was attached to the object with one owned by the addon to ensure that the
object has the right type.
If the object already has an associated type tag, this API will return
napi_invalid_arg
napi_check_object_type_tag
Added in: v14.8.0, v12.19.0
N-API Version:
napi_status
napi_check_object_type_tag
napi_env
env
napi_value
js_object
const
napi_type_tag
type_tag
bool
result
);
[in] env
: The environment that the API is invoked under.
[in] js_object
: The JavaScript object or
external
whose type tag to
examine.
[in] type_tag
: The tag with which to compare any tag found on the object.
[out] result
: Whether the type tag given matched the type tag on the
object.
false
is also returned if no type tag was found on the object.
Returns
napi_ok
if the API succeeded.
Compares the pointer given as
type_tag
with any that can be found on
js_object
. If no tag is found on
js_object
or, if a tag is found but it does
not match
type_tag
, then
result
is set to
false
. If a tag is found and it
matches
type_tag
, then
result
is set to
true
napi_add_finalizer
Added in: v8.0.0
N-API Version:
napi_status
napi_add_finalizer
napi_env
env
napi_value
js_object
void
finalize_data
node_api_basic_finalize
finalize_cb
void
finalize_hint
napi_ref
result
);
[in] env
: The environment that the API is invoked under.
[in] js_object
: The JavaScript object to which the native data will be
attached.
[in] finalize_data
: Optional data to be passed to
finalize_cb
[in] finalize_cb
: Native callback that will be used to free the
native data when the JavaScript object has been garbage-collected.
napi_finalize
provides more details.
[in] finalize_hint
: Optional contextual hint that is passed to the
finalize callback.
[out] result
: Optional reference to the JavaScript object.
Returns
napi_ok
if the API succeeded.
Adds a
napi_finalize
callback which will be called when the JavaScript object
in
js_object
has been garbage-collected.
This API can be called multiple times on a single JavaScript object.
Caution
: The optional returned reference (if obtained) should be deleted via
napi_delete_reference
ONLY in response to the finalize callback
invocation. If it is deleted before then, then the finalize callback may never
be invoked. Therefore, when obtaining a reference a finalize callback is also
required in order to enable correct disposal of the reference.
node_api_post_finalizer
Added in: v21.0.0, v20.10.0, v18.19.0
Stability: 1 - Experimental
napi_status
node_api_post_finalizer
node_api_basic_env
env
napi_finalize
finalize_cb
void
finalize_data
void
finalize_hint
);
[in] env
: The environment that the API is invoked under.
[in] finalize_cb
: Native callback that will be used to free the
native data when the JavaScript object has been garbage-collected.
napi_finalize
provides more details.
[in] finalize_data
: Optional data to be passed to
finalize_cb
[in] finalize_hint
: Optional contextual hint that is passed to the
finalize callback.
Returns
napi_ok
if the API succeeded.
Schedules a
napi_finalize
callback to be called asynchronously in the
event loop.
Normally, finalizers are called while the GC (garbage collector) collects
objects. At that point calling any Node-API that may cause changes in the GC
state will be disabled and will crash Node.js.
node_api_post_finalizer
helps to work around this limitation by allowing the
add-on to defer calls to such Node-APIs to a point in time outside of the GC
finalization.
Simple asynchronous operations
Addon modules often need to leverage async helpers from libuv as part of their
implementation. This allows them to schedule work to be executed asynchronously
so that their methods can return in advance of the work being completed. This
allows them to avoid blocking overall execution of the Node.js application.
Node-API provides an ABI-stable interface for these
supporting functions which covers the most common asynchronous use cases.
Node-API defines the
napi_async_work
structure which is used to manage
asynchronous workers. Instances are created/deleted with
napi_create_async_work
and
napi_delete_async_work
The
execute
and
complete
callbacks are functions that will be
invoked when the executor is ready to execute and when it completes its
task respectively.
The
execute
function should avoid making any Node-API calls
that could result in the execution of JavaScript or interaction with
JavaScript objects. Most often, any code that needs to make Node-API
calls should be made in
complete
callback instead.
Avoid using the
napi_env
parameter in the execute callback as
it will likely execute JavaScript.
These functions implement the following interfaces:
typedef
void
napi_async_execute_callback
)(
napi_env env
void
data
);
typedef
void
napi_async_complete_callback
)(
napi_env env
napi_status status
void
data
);
When these methods are invoked, the
data
parameter passed will be the
addon-provided
void*
data that was passed into the
napi_create_async_work
call.
Once created the async worker can be queued
for execution using the
napi_queue_async_work
function:
napi_status
napi_queue_async_work
node_api_basic_env
env
napi_async_work
work
);
napi_cancel_async_work
can be used if the work needs
to be cancelled before the work has started execution.
After calling
napi_cancel_async_work
, the
complete
callback
will be invoked with a status value of
napi_cancelled
The work should not be deleted before the
complete
callback invocation, even when it was cancelled.
napi_create_async_work
Added in: v8.0.0
N-API Version:
History
Version
Changes
v8.6.0
Added
async_resource
and
async_resource_name
parameters.
napi_status
napi_create_async_work
napi_env
env
napi_value
async_resource
napi_value
async_resource_name
napi_async_execute_callback
execute
napi_async_complete_callback
complete
void
data
napi_async_work
result
);
[in] env
: The environment that the API is invoked under.
[in] async_resource
: An optional object associated with the async work
that will be passed to possible
async_hooks
init
hooks
[in] async_resource_name
: Identifier for the kind of resource that is being
provided for diagnostic information exposed by the
async_hooks
API.
[in] execute
: The native function which should be called to execute the
logic asynchronously. The given function is called from a worker pool thread
and can execute in parallel with the main event loop thread.
[in] complete
: The native function which will be called when the
asynchronous logic is completed or is cancelled. The given function is called
from the main event loop thread.
napi_async_complete_callback
provides
more details.
[in] data
: User-provided data context. This will be passed back into the
execute and complete functions.
[out] result
napi_async_work*
which is the handle to the newly created
async work.
Returns
napi_ok
if the API succeeded.
This API allocates a work object that is used to execute logic asynchronously.
It should be freed using
napi_delete_async_work
once the work is no longer
required.
async_resource_name
should be a null-terminated, UTF-8-encoded string.
The
async_resource_name
identifier is provided by the user and should be
representative of the type of async work being performed. It is also recommended
to apply namespacing to the identifier, e.g. by including the module name. See
the
async_hooks
documentation
for more information.
napi_delete_async_work
Added in: v8.0.0
N-API Version:
napi_status
napi_delete_async_work
napi_env
env
napi_async_work
work
);
[in] env
: The environment that the API is invoked under.
[in] work
: The handle returned by the call to
napi_create_async_work
Returns
napi_ok
if the API succeeded.
This API frees a previously allocated work object.
This API can be called even if there is a pending JavaScript exception.
napi_queue_async_work
Added in: v8.0.0
N-API Version:
napi_status
napi_queue_async_work
node_api_basic_env
env
napi_async_work
work
);
[in] env
: The environment that the API is invoked under.
[in] work
: The handle returned by the call to
napi_create_async_work
Returns
napi_ok
if the API succeeded.
This API requests that the previously allocated work be scheduled
for execution. Once it returns successfully, this API must not be called again
with the same
napi_async_work
item or the result will be undefined.
napi_cancel_async_work
Added in: v8.0.0
N-API Version:
napi_status
napi_cancel_async_work
node_api_basic_env
env
napi_async_work
work
);
[in] env
: The environment that the API is invoked under.
[in] work
: The handle returned by the call to
napi_create_async_work
Returns
napi_ok
if the API succeeded.
This API cancels queued work if it has not yet
been started. If it has already started executing, it cannot be
cancelled and
napi_generic_failure
will be returned. If successful,
the
complete
callback will be invoked with a status value of
napi_cancelled
. The work should not be deleted before the
complete
callback invocation, even if it has been successfully cancelled.
This API can be called even if there is a pending JavaScript exception.
Custom asynchronous operations
The simple asynchronous work APIs above may not be appropriate for every
scenario. When using any other asynchronous mechanism, the following APIs
are necessary to ensure an asynchronous operation is properly tracked by
the runtime.
napi_async_init
Added in: v8.6.0
N-API Version:
History
Version
Changes
v25.0.0
The
async_resource
object will now be held as a strong reference.
napi_status
napi_async_init
napi_env
env
napi_value
async_resource
napi_value
async_resource_name
napi_async_context
result
[in] env
: The environment that the API is invoked under.
[in] async_resource
: Object associated with the async work
that will be passed to possible
async_hooks
init
hooks
and can be
accessed by
async_hooks.executionAsyncResource()
[in] async_resource_name
: Identifier for the kind of resource that is being
provided for diagnostic information exposed by the
async_hooks
API.
[out] result
: The initialized async context.
Returns
napi_ok
if the API succeeded.
In order to retain ABI compatibility with previous versions, passing
NULL
for
async_resource
does not result in an error. However, this is not
recommended as this will result in undesirable behavior with
async_hooks
init
hooks
and
async_hooks.executionAsyncResource()
as the resource is
now required by the underlying
async_hooks
implementation in order to provide
the linkage between async callbacks.
Previous versions of this API were not maintaining a strong reference to
async_resource
while the
napi_async_context
object existed and instead
expected the caller to hold a strong reference. This has been changed, as a
corresponding call to
napi_async_destroy
for every call to
napi_async_init()
is a requirement in any case to avoid memory leaks.
napi_async_destroy
Added in: v8.6.0
N-API Version:
napi_status
napi_async_destroy
napi_env
env
napi_async_context
async_context
);
[in] env
: The environment that the API is invoked under.
[in] async_context
: The async context to be destroyed.
Returns
napi_ok
if the API succeeded.
This API can be called even if there is a pending JavaScript exception.
napi_make_callback
Added in: v8.0.0
N-API Version:
History
Version
Changes
v8.6.0
Added
async_context
parameter.
NAPI_EXTERN napi_status
napi_make_callback
napi_env
env
napi_async_context
async_context
napi_value
recv
napi_value
func
size_t
argc
const
napi_value
argv
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] async_context
: Context for the async operation that is
invoking the callback. This should normally be a value previously
obtained from
napi_async_init
In order to retain ABI compatibility with previous versions, passing
NULL
for
async_context
does not result in an error. However, this results
in incorrect operation of async hooks. Potential issues include loss of
async context when using the
AsyncLocalStorage
API.
[in] recv
: The
this
value passed to the called function.
[in] func
napi_value
representing the JavaScript function to be invoked.
[in] argc
: The count of elements in the
argv
array.
[in] argv
: Array of JavaScript values as
napi_value
representing the
arguments to the function. If
argc
is zero this parameter may be
omitted by passing in
NULL
[out] result
napi_value
representing the JavaScript object returned.
Returns
napi_ok
if the API succeeded.
This method allows a JavaScript function object to be called from a native
add-on. This API is similar to
napi_call_function
. However, it is used to call
from
native code back
into
JavaScript
after
returning from an async
operation (when there is no other script on the stack). It is a fairly simple
wrapper around
node::MakeCallback
Note it is
not
necessary to use
napi_make_callback
from within a
napi_async_complete_callback
; in that situation the callback's async
context has already been set up, so a direct call to
napi_call_function
is sufficient and appropriate. Use of the
napi_make_callback
function
may be required when implementing custom async behavior that does not use
napi_create_async_work
Any
process.nextTick
s or Promises scheduled on the microtask queue by
JavaScript during the callback are ran before returning back to C/C++.
napi_open_callback_scope
Added in: v9.6.0
N-API Version:
NAPI_EXTERN napi_status
napi_open_callback_scope
napi_env
env
napi_value
resource_object
napi_async_context
context
napi_callback_scope
result
[in] env
: The environment that the API is invoked under.
[in] resource_object
: An object associated with the async work
that will be passed to possible
async_hooks
init
hooks
. This
parameter has been deprecated and is ignored at runtime. Use the
async_resource
parameter in
napi_async_init
instead.
[in] context
: Context for the async operation that is invoking the callback.
This should be a value previously obtained from
napi_async_init
[out] result
: The newly created scope.
There are cases (for example, resolving promises) where it is
necessary to have the equivalent of the scope associated with a callback
in place when making certain Node-API calls. If there is no other script on
the stack the
napi_open_callback_scope
and
napi_close_callback_scope
functions can be used to open/close
the required scope.
napi_close_callback_scope
Added in: v9.6.0
N-API Version:
NAPI_EXTERN napi_status
napi_close_callback_scope
napi_env
env
napi_callback_scope
scope
[in] env
: The environment that the API is invoked under.
[in] scope
: The scope to be closed.
This API can be called even if there is a pending JavaScript exception.
Version management
napi_get_node_version
Added in: v8.4.0
N-API Version:
typedef
struct
uint32_t
major
uint32_t
minor
uint32_t
patch
const
char
release
napi_node_version
napi_status
napi_get_node_version
node_api_basic_env
env
const
napi_node_version
**
version
);
[in] env
: The environment that the API is invoked under.
[out] version
: A pointer to version information for Node.js itself.
Returns
napi_ok
if the API succeeded.
This function fills the
version
struct with the major, minor, and patch
version of Node.js that is currently running, and the
release
field with the
value of
process.release.name
The returned buffer is statically allocated and does not need to be freed.
napi_get_version
Added in: v8.0.0
N-API Version:
napi_status
napi_get_version
node_api_basic_env
env
uint32_t
result
);
[in] env
: The environment that the API is invoked under.
[out] result
: The highest version of Node-API supported.
Returns
napi_ok
if the API succeeded.
This API returns the highest Node-API version supported by the
Node.js runtime. Node-API is planned to be additive such that
newer releases of Node.js may support additional API functions.
In order to allow an addon to use a newer function when running with
versions of Node.js that support it, while providing
fallback behavior when running with Node.js versions that don't
support it:
Call
napi_get_version()
to determine if the API is available.
If available, dynamically load a pointer to the function using
uv_dlsym()
Use the dynamically loaded pointer to invoke the function.
If the function is not available, provide an alternate implementation
that does not use the function.
Memory management
napi_adjust_external_memory
Added in: v8.5.0
N-API Version:
NAPI_EXTERN napi_status
napi_adjust_external_memory
node_api_basic_env
env
int64_t
change_in_bytes
int64_t
result
);
[in] env
: The environment that the API is invoked under.
[in] change_in_bytes
: The change in externally allocated memory that is kept
alive by JavaScript objects.
[out] result
: The adjusted value. This value should reflect the
total amount of external memory with the given
change_in_bytes
included.
The absolute value of the returned value should not be depended on.
For example, implementations may use a single counter for all addons, or a
counter for each addon.
Returns
napi_ok
if the API succeeded.
This function gives the runtime an indication of the amount of externally
allocated memory that is kept alive by JavaScript objects
(i.e. a JavaScript object that points to its own memory allocated by a
native addon). Registering externally allocated memory may, but is not
guaranteed to, trigger global garbage collections more
often than it would otherwise.
This function is expected to be called in a manner such that an
addon does not decrease the external memory more than it has
increased the external memory.
Promises
Node-API provides facilities for creating
Promise
objects as described in
Section Promise objects
of the ECMA specification. It implements promises as a pair of
objects. When a promise is created by
napi_create_promise()
, a "deferred"
object is created and returned alongside the
Promise
. The deferred object is
bound to the created
Promise
and is the only means to resolve or reject the
Promise
using
napi_resolve_deferred()
or
napi_reject_deferred()
. The
deferred object that is created by
napi_create_promise()
is freed by
napi_resolve_deferred()
or
napi_reject_deferred()
. The
Promise
object may
be returned to JavaScript where it can be used in the usual fashion.
For example, to create a promise and pass it to an asynchronous worker:
napi_deferred deferred
napi_value promise
napi_status status
// Create the promise.
status
napi_create_promise
env
deferred
promise
);
if
status
!=
napi_ok
return
NULL
// Pass the deferred to a function that performs an asynchronous action.
do_something_asynchronous
deferred
);
// Return the promise to JS
return
promise
The above function
do_something_asynchronous()
would perform its asynchronous
action and then it would resolve or reject the deferred, thereby concluding the
promise and freeing the deferred:
napi_deferred deferred
napi_value undefined
napi_status status
// Create a value with which to conclude the deferred.
status
napi_get_undefined
env
undefined
);
if
status
!=
napi_ok
return
NULL
// Resolve or reject the promise associated with the deferred depending on
// whether the asynchronous action succeeded.
if
asynchronous_action_succeeded
status
napi_resolve_deferred
env
deferred
undefined
);
else
status
napi_reject_deferred
env
deferred
undefined
);
if
status
!=
napi_ok
return
NULL
// At this point the deferred has been freed, so we should assign NULL to it.
deferred
NULL
napi_create_promise
Added in: v8.5.0
N-API Version:
napi_status
napi_create_promise
napi_env
env
napi_deferred
deferred
napi_value
promise
);
[in] env
: The environment that the API is invoked under.
[out] deferred
: A newly created deferred object which can later be passed to
napi_resolve_deferred()
or
napi_reject_deferred()
to resolve resp. reject
the associated promise.
[out] promise
: The JavaScript promise associated with the deferred object.
Returns
napi_ok
if the API succeeded.
This API creates a deferred object and a JavaScript promise.
napi_resolve_deferred
Added in: v8.5.0
N-API Version:
napi_status
napi_resolve_deferred
napi_env
env
napi_deferred
deferred
napi_value
resolution
);
[in] env
: The environment that the API is invoked under.
[in] deferred
: The deferred object whose associated promise to resolve.
[in] resolution
: The value with which to resolve the promise.
This API resolves a JavaScript promise by way of the deferred object
with which it is associated. Thus, it can only be used to resolve JavaScript
promises for which the corresponding deferred object is available. This
effectively means that the promise must have been created using
napi_create_promise()
and the deferred object returned from that call must
have been retained in order to be passed to this API.
The deferred object is freed upon successful completion.
napi_reject_deferred
Added in: v8.5.0
N-API Version:
napi_status
napi_reject_deferred
napi_env
env
napi_deferred
deferred
napi_value
rejection
);
[in] env
: The environment that the API is invoked under.
[in] deferred
: The deferred object whose associated promise to resolve.
[in] rejection
: The value with which to reject the promise.
This API rejects a JavaScript promise by way of the deferred object
with which it is associated. Thus, it can only be used to reject JavaScript
promises for which the corresponding deferred object is available. This
effectively means that the promise must have been created using
napi_create_promise()
and the deferred object returned from that call must
have been retained in order to be passed to this API.
The deferred object is freed upon successful completion.
napi_is_promise
Added in: v8.5.0
N-API Version:
napi_status
napi_is_promise
napi_env
env
napi_value
value
bool
is_promise
);
[in] env
: The environment that the API is invoked under.
[in] value
: The value to examine
[out] is_promise
: Flag indicating whether
promise
is a native promise
object (that is, a promise object created by the underlying engine).
Script execution
Node-API provides an API for executing a string containing JavaScript using the
underlying JavaScript engine.
napi_run_script
Added in: v8.5.0
N-API Version:
NAPI_EXTERN napi_status
napi_run_script
napi_env
env
napi_value
script
napi_value
result
);
[in] env
: The environment that the API is invoked under.
[in] script
: A JavaScript string containing the script to execute.
[out] result
: The value resulting from having executed the script.
This function executes a string of JavaScript code and returns its result with
the following caveats:
Unlike
eval
, this function does not allow the script to access the current
lexical scope, and therefore also does not allow to access the
module scope
, meaning that pseudo-globals such as
require
will not be
available.
The script can access the
global scope
. Function and
var
declarations
in the script will be added to the
global
object. Variable declarations
made using
let
and
const
will be visible globally, but will not be added
to the
global
object.
The value of
this
is
global
within the script.
libuv event loop
Node-API provides a function for getting the current event loop associated with
a specific
napi_env
napi_get_uv_event_loop
Added in: v9.3.0, v8.10.0
N-API Version:
NAPI_EXTERN napi_status
napi_get_uv_event_loop
node_api_basic_env
env
struct
uv_loop_s
**
loop
);
[in] env
: The environment that the API is invoked under.
[out] loop
: The current libuv loop instance.
Note: While libuv has been relatively stable over time, it does
not provide an ABI stability guarantee. Use of this function should be avoided.
Its use may result in an addon that does not work across Node.js versions.
asynchronous-thread-safe-function-calls
are an alternative for many use cases.
Asynchronous thread-safe function calls
JavaScript functions can normally only be called from a native addon's main
thread. If an addon creates additional threads, then Node-API functions that
require a
napi_env
napi_value
, or
napi_ref
must not be called from those
threads.
When an addon has additional threads and JavaScript functions need to be invoked
based on the processing completed by those threads, those threads must
communicate with the addon's main thread so that the main thread can invoke the
JavaScript function on their behalf. The thread-safe function APIs provide an
easy way to do this.
These APIs provide the type
napi_threadsafe_function
as well as APIs to
create, destroy, and call objects of this type.
napi_create_threadsafe_function()
creates a persistent reference to a
napi_value
that holds a JavaScript function which can be called from multiple
threads. The calls happen asynchronously. This means that values with which the
JavaScript callback is to be called will be placed in a queue, and, for each
value in the queue, a call will eventually be made to the JavaScript function.
Upon creation of a
napi_threadsafe_function
napi_finalize
callback can be
provided. This callback will be invoked on the main thread when the thread-safe
function is about to be destroyed. It receives the context and the finalize data
given during construction, and provides an opportunity for cleaning up after the
threads e.g. by calling
uv_thread_join()
Aside from the main loop thread,
no threads should be using the thread-safe function after the finalize callback
completes.
The
context
given during the call to
napi_create_threadsafe_function()
can
be retrieved from any thread with a call to
napi_get_threadsafe_function_context()
Calling a thread-safe function
napi_call_threadsafe_function()
can be used for initiating a call into
JavaScript.
napi_call_threadsafe_function()
accepts a parameter which controls
whether the API behaves blockingly. If set to
napi_tsfn_nonblocking
, the API
behaves non-blockingly, returning
napi_queue_full
if the queue was full,
preventing data from being successfully added to the queue. If set to
napi_tsfn_blocking
, the API blocks until space becomes available in the queue.
napi_call_threadsafe_function()
never blocks if the thread-safe function was
created with a maximum queue size of 0.
napi_call_threadsafe_function()
should not be called with
napi_tsfn_blocking
from a JavaScript thread, because, if the queue is full, it may cause the
JavaScript thread to deadlock.
The actual call into JavaScript is controlled by the callback given via the
call_js_cb
parameter.
call_js_cb
is invoked on the main thread once for each
value that was placed into the queue by a successful call to
napi_call_threadsafe_function()
. If such a callback is not given, a default
callback will be used, and the resulting JavaScript call will have no arguments.
The
call_js_cb
callback receives the JavaScript function to call as a
napi_value
in its parameters, as well as the
void*
context pointer used when
creating the
napi_threadsafe_function
, and the next data pointer that was
created by one of the secondary threads. The callback can then use an API such
as
napi_call_function()
to call into JavaScript.
The callback may also be invoked with
env
and
call_js_cb
both set to
NULL
to indicate that calls into JavaScript are no longer possible, while items
remain in the queue that may need to be freed. This normally occurs when the
Node.js process exits while there is a thread-safe function still active.
It is not necessary to call into JavaScript via
napi_make_callback()
because
Node-API runs
call_js_cb
in a context appropriate for callbacks.
Zero or more queued items may be invoked in each tick of the event loop.
Applications should not depend on a specific behavior other than progress in
invoking callbacks will be made and events will be invoked
as time moves forward.
Reference counting of thread-safe functions
Threads can be added to and removed from a
napi_threadsafe_function
object
during its existence. Thus, in addition to specifying an initial number of
threads upon creation,
napi_acquire_threadsafe_function
can be called to
indicate that a new thread will start making use of the thread-safe function.
Similarly,
napi_release_threadsafe_function
can be called to indicate that an
existing thread will stop making use of the thread-safe function.
napi_threadsafe_function
objects are destroyed when every thread which uses
the object has called
napi_release_threadsafe_function()
or has received a
return status of
napi_closing
in response to a call to
napi_call_threadsafe_function
. The queue is emptied before the
napi_threadsafe_function
is destroyed.
napi_release_threadsafe_function()
should be the last API call made in conjunction with a given
napi_threadsafe_function
, because after the call completes, there is no
guarantee that the
napi_threadsafe_function
is still allocated. For the same
reason, do not use a thread-safe function
after receiving a return value of
napi_closing
in response to a call to
napi_call_threadsafe_function
. Data associated with the
napi_threadsafe_function
can be freed in its
napi_finalize
callback which
was passed to
napi_create_threadsafe_function()
. The parameter
initial_thread_count
of
napi_create_threadsafe_function
marks the initial
number of acquisitions of the thread-safe functions, instead of calling
napi_acquire_threadsafe_function
multiple times at creation.
Once the number of threads making use of a
napi_threadsafe_function
reaches
zero, no further threads can start making use of it by calling
napi_acquire_threadsafe_function()
. In fact, all subsequent API calls
associated with it, except
napi_release_threadsafe_function()
, will return an
error value of
napi_closing
The thread-safe function can be "aborted" by giving a value of
napi_tsfn_abort
to
napi_release_threadsafe_function()
. This will cause all subsequent APIs
associated with the thread-safe function except
napi_release_threadsafe_function()
to return
napi_closing
even before its
reference count reaches zero. In particular,
napi_call_threadsafe_function()
will return
napi_closing
, thus informing the threads that it is no longer
possible to make asynchronous calls to the thread-safe function. This can be
used as a criterion for terminating the thread.
Upon receiving a return value
of
napi_closing
from
napi_call_threadsafe_function()
a thread must not use
the thread-safe function anymore because it is no longer guaranteed to
be allocated.
Deciding whether to keep the process running
Similarly to libuv handles, thread-safe functions can be "referenced" and
"unreferenced". A "referenced" thread-safe function will cause the event loop on
the thread on which it is created to remain alive until the thread-safe function
is destroyed. In contrast, an "unreferenced" thread-safe function will not
prevent the event loop from exiting. The APIs
napi_ref_threadsafe_function
and
napi_unref_threadsafe_function
exist for this purpose.
Neither does
napi_unref_threadsafe_function
mark the thread-safe functions as
able to be destroyed nor does
napi_ref_threadsafe_function
prevent it from
being destroyed.
napi_create_threadsafe_function
Added in: v10.6.0
N-API Version:
History
Version
Changes
v12.6.0, v10.17.0
Made
func
parameter optional with custom
call_js_cb
NAPI_EXTERN napi_status
napi_create_threadsafe_function
napi_env
env
napi_value
func
napi_value
async_resource
napi_value
async_resource_name
size_t
max_queue_size
size_t
initial_thread_count
void
thread_finalize_data
napi_finalize
thread_finalize_cb
void
context
napi_threadsafe_function_call_js
call_js_cb
napi_threadsafe_function
result
);
[in] env
: The environment that the API is invoked under.
[in] func
: An optional JavaScript function to call from another thread. It
must be provided if
NULL
is passed to
call_js_cb
[in] async_resource
: An optional object associated with the async work that
will be passed to possible
async_hooks
init
hooks
[in] async_resource_name
: A JavaScript string to provide an identifier for
the kind of resource that is being provided for diagnostic information exposed
by the
async_hooks
API.
[in] max_queue_size
: Maximum size of the queue.
for no limit.
[in] initial_thread_count
: The initial number of acquisitions, i.e. the
initial number of threads, including the main thread, which will be making use
of this function.
[in] thread_finalize_data
: Optional data to be passed to
thread_finalize_cb
[in] thread_finalize_cb
: Optional function to call when the
napi_threadsafe_function
is being destroyed.
[in] context
: Optional data to attach to the resulting
napi_threadsafe_function
[in] call_js_cb
: Optional callback which calls the JavaScript function in
response to a call on a different thread. This callback will be called on the
main thread. If not given, the JavaScript function will be called with no
parameters and with
undefined
as its
this
value.
napi_threadsafe_function_call_js
provides more details.
[out] result
: The asynchronous thread-safe JavaScript function.
Change History:
Version 10 (
NAPI_VERSION
is defined as
10
or higher):
Uncaught exceptions thrown in
call_js_cb
are handled with the
'uncaughtException'
event, instead of being ignored.
napi_get_threadsafe_function_context
Added in: v10.6.0
N-API Version:
NAPI_EXTERN napi_status
napi_get_threadsafe_function_context
napi_threadsafe_function
func
void
**
result
);
[in] func
: The thread-safe function for which to retrieve the context.
[out] result
: The location where to store the context.
This API may be called from any thread which makes use of
func
napi_call_threadsafe_function
Added in: v10.6.0
N-API Version:
History
Version
Changes
v14.5.0
Support for
napi_would_deadlock
has been reverted.
v14.1.0
Return
napi_would_deadlock
when called with
napi_tsfn_blocking
from the main thread or a worker thread and the queue is full.
NAPI_EXTERN napi_status
napi_call_threadsafe_function
napi_threadsafe_function
func
void
data
napi_threadsafe_function_call_mode
is_blocking
);
[in] func
: The asynchronous thread-safe JavaScript function to invoke.
[in] data
: Data to send into JavaScript via the callback
call_js_cb
provided during the creation of the thread-safe JavaScript function.
[in] is_blocking
: Flag whose value can be either
napi_tsfn_blocking
to
indicate that the call should block if the queue is full or
napi_tsfn_nonblocking
to indicate that the call should return immediately
with a status of
napi_queue_full
whenever the queue is full.
This API should not be called with
napi_tsfn_blocking
from a JavaScript
thread, because, if the queue is full, it may cause the JavaScript thread to
deadlock.
This API will return
napi_closing
if
napi_release_threadsafe_function()
was
called with
abort
set to
napi_tsfn_abort
from any thread. The value is only
added to the queue if the API returns
napi_ok
This API may be called from any thread which makes use of
func
napi_acquire_threadsafe_function
Added in: v10.6.0
N-API Version:
NAPI_EXTERN napi_status
napi_acquire_threadsafe_function
napi_threadsafe_function
func
);
[in] func
: The asynchronous thread-safe JavaScript function to start making
use of.
A thread should call this API before passing
func
to any other thread-safe
function APIs to indicate that it will be making use of
func
. This prevents
func
from being destroyed when all other threads have stopped making use of
it.
This API may be called from any thread which will start making use of
func
napi_release_threadsafe_function
Added in: v10.6.0
N-API Version:
NAPI_EXTERN napi_status
napi_release_threadsafe_function
napi_threadsafe_function
func
napi_threadsafe_function_release_mode
mode
);
[in] func
: The asynchronous thread-safe JavaScript function whose reference
count to decrement.
[in] mode
: Flag whose value can be either
napi_tsfn_release
to indicate
that the current thread will make no further calls to the thread-safe
function, or
napi_tsfn_abort
to indicate that in addition to the current
thread, no other thread should make any further calls to the thread-safe
function. If set to
napi_tsfn_abort
, further calls to
napi_call_threadsafe_function()
will return
napi_closing
, and no further
values will be placed in the queue.
A thread should call this API when it stops making use of
func
. Passing
func
to any thread-safe APIs after having called this API has undefined results, as
func
may have been destroyed.
This API may be called from any thread which will stop making use of
func
napi_ref_threadsafe_function
Added in: v10.6.0
N-API Version:
NAPI_EXTERN napi_status
napi_ref_threadsafe_function
node_api_basic_env
env
napi_threadsafe_function
func
);
[in] env
: The environment that the API is invoked under.
[in] func
: The thread-safe function to reference.
This API is used to indicate that the event loop running on the main thread
should not exit until
func
has been destroyed. Similar to
uv_ref
it is
also idempotent.
Neither does
napi_unref_threadsafe_function
mark the thread-safe functions as
able to be destroyed nor does
napi_ref_threadsafe_function
prevent it from
being destroyed.
napi_acquire_threadsafe_function
and
napi_release_threadsafe_function
are available for that purpose.
This API may only be called from the main thread.
napi_unref_threadsafe_function
Added in: v10.6.0
N-API Version:
NAPI_EXTERN napi_status
napi_unref_threadsafe_function
node_api_basic_env
env
napi_threadsafe_function
func
);
[in] env
: The environment that the API is invoked under.
[in] func
: The thread-safe function to unreference.
This API is used to indicate that the event loop running on the main thread
may exit before
func
is destroyed. Similar to
uv_unref
it is also
idempotent.
This API may only be called from the main thread.
Miscellaneous utilities
node_api_get_module_file_name
Added in: v15.9.0, v14.18.0, v12.22.0
N-API Version:
NAPI_EXTERN napi_status
node_api_get_module_file_name
node_api_basic_env
env
const
char
**
result
);
[in] env
: The environment that the API is invoked under.
[out] result
: A URL containing the absolute path of the
location from which the add-on was loaded. For a file on the local
file system it will start with
file://
. The string is null-terminated and
owned by
env
and must thus not be modified or freed.
result
may be an empty string if the add-on loading process fails to establish
the add-on's file name during loading.