Node-API Data Types and APIs
Data Types
napi_status
Enum indicating the execution status of a Node-API call.
Each time a Node-API function is called, a value of napi_status is returned indicating the execution result.
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;
napi_extended_error_info
Struct that holds detailed error information when a Node-API call fails.
typedef struct {
const char *error_message;
void *engine_reserved;
uint32_t engine_error_code;
napi_status error_code;
} napi_extended_error_info;
napi_value
A JavaScript (JS) value in C++.
napi_env
-
Context used by the underlying Node-API implementation. It is passed to the native functions when they are invoked, and must be passed back when Node-API calls are made.
-
napi_env becomes invalid when the JS thread bound with napi_env exits.
-
Avoid caching napi_env or passing napi_env between instances of the same addon running on different worker threads.
napi_threadsafe_function
Pointer that represents a JS function that can be called asynchronously from multiple threads. It can be used to pass the asynchronous (async for short) operation result to the JS environment, such as reading data from another thread or performing compute-intensive operations. In addition, it can be used to call functions in C++ code from a JS environment for execution in another thread. By using napi_threadsafe_function, you can implement efficient interaction between JS and C++ code while maintaining thread safety.
napi_threadsafe_function_release_mode
Enum that indicates when to release the thread-safe function.
typedef enum {
napi_tsfn_release,
napi_tsfn_abort
} napi_threadsafe_function_release_mode;
Its value is passed to napi_release_threadsafe_function.
napi_release_threadsafe_function(napi_threadsafe_function func,
napi_threadsafe_function_release_mode mode);
-
If the value is napi_tsfn_release, the current thread will not call this thread-safe function.
-
If the value is napi_tsfn_abort, only the current thread can call this thread-safe function. In this case, using napi_call_threadsafe_function to call this function will return napi_closing, and this function will not be placed in the queue.
napi_threadsafe_function_call_mode
Enum that indicates whether the call should be blocked when the queue associated with the thread-safe function is full.
The data struct is as follows:
typedef enum {
napi_tsfn_nonblocking,
napi_tsfn_blocking
} napi_threadsafe_function_call_mode;
-
napi_tsfn_nonblocking: Leave napi_call_threadsafe_function unblocked. If the queue is full, napi_queue_full is returned to prevent data from being added to the queue.
-
napi_tsfn_blocking: Block napi_call_threadsafe_function until there is available space in the queue.
Memory Management Types
Node-API provides the following memory management types:
napi_handle_scope
Data used to manage the lifecycle of JS objects. It allows JS objects to remain active within a certain range for use in JS code. When napi_handle_scope is created, all JS objects created in this range remain active until the end. This can prevent released objects from being used in JS code, which improves code reliability and performance.
napi_escapable_handle_scope
-
It is created by napi_open_escapable_handle_scope and closed by napi_close_escapable_handle_scope.
-
It is a special type of handle range used to return values created within the scope of escapable_handle_scope to a parent scope.
-
You can use napi_escape_handle to promote escape_handle_scope to a JS object so that it is valid for the lifetime of the outer scope.
napi_ref
Reference to napi_value, which allows you to manage the lifecycle of JS values.
napi_type_tag
Struct containing two unsigned 64-bit integers to identify the type of a Node-API value.
typedef struct {
uint64_t lower;
uint64_t upper;
} napi_type_tag;
-
It is a 128-bit value stored as two unsigned 64-bit integers. It is used to tag JS objects to ensure that they are of a certain type.
-
This is a stronger check than napi_instanceof because napi_instanceof may report a false positive if the object's prototype is manipulated.
-
The combination of type_tag and napi_wrap is useful because it ensures that the pointer retrieved from a wrapped object can be safely converted to the native type corresponding to the type tag that had been previously applied to the JS object.
napi_async_cleanup_hook_handle
Value used to register a callback for an async operation. It is mainly used to perform a cleanup operation when an async operation is complete or canceled, for example, releasing a resource or canceling an operation. Using napi_async_cleanup_hook_handle ensures that related resources are correctly released and cleaned up when an async operation is complete or canceled, thereby avoiding problems such as memory leakage.
Callback Types
Node-API provides the following callback types:
napi_callback_info
Data type passed to napi_get_cb_info to obtain JS input parameters.
napi_callback
User-defined native function, which is exposed to JS via Node-API. Generally, no handle or callback scope is created inside this callback.
The basic usage is as follows:
typedef napi_value (*napi_callback)(napi_env, napi_callback_info);
napi_finalize
Function pointer passed to napi_create_threadsafe_function and napi_set_instance_data. napi_finalize is called when an object is reclaimed.
napi_async_execute_callback
Function pointer used in napi_create_async_work.
-
An async native function is called from a worker pool thread and can be executed in parallel with the main event loop thread.
-
Avoid making Node-API calls that execute JS code or interact with JS objects when implementing this callback.
-
Node-API calls should be executed in napi_async_complete_callback.
napi_async_complete_callback
Function pointer used when an async operation is complete. When an async operation is required, you can use napi_create_async_work to create an async work and specify napi_async_complete_callback. When the async work is complete, the callback will be automatically invoked for subsequent processing. Parameters of the callback include the status of the async operation and a return value, based on which corresponding processing can be performed.
napi_threadsafe_function_call_js
Function pointer used in the main thread to interact with the JS code in an independent thread to implement more complex scenarios. It is used in napi_create_threadsafe_function(napi_env env, ..., napi_threadsafe_function_call_js call_js_cb, ...).
napi_cleanup_hook
Function pointer used with napi_add_env_cleanup_hook. It will be called when the environment is destroyed.
napi_async_cleanup_hook
Function pointer used with napi_add_async_cleanup_hook. It will be called when the environment is destroyed.
QoS
Enum indicating the thread scheduling priority.
typedef enum {
napi_qos_background = 0,
napi_qos_utility = 1,
napi_qos_default = 2,
napi_qos_user_initiated = 3,
} napi_qos_t;
| QoS | Use Scenario |
|---|---|
| napi_qos_background | Low priority for works invisible to users, such as data synchronization and backup. |
| napi_qos_utility | Medium priority for works that do not require immediate response, such as downloading or importing data. |
| napi_qos_default | Default priority. |
| napi_qos_user_initiated | High priority for user-triggered works with visible progress, for example, opening a file. |
APIs
Node-API is extended based on the native modules provided by Node.js. The following lists the APIs supported currently.
Async Thread-Safe APIs
| API | Description |
|---|---|
| napi_create_threadsafe_function | Creates a thread-safe function. |
| napi_get_threadsafe_function_context | Obtains the context of a thread-safe function. |
| napi_call_threadsafe_function | Calls a thread-safe function. |
| napi_acquire_threadsafe_function | Acquires a thread-safe function. |
| napi_release_threadsafe_function | Releases a thread-safe function. |
| napi_ref_threadsafe_function | Indicates that the event loop running on the main thread should not exit until the thread-safe function is destroyed. |
| napi_unref_threadsafe_function | Indicates that the event loop running on the main thread may exit before the thread-safe function is destroyed. |
Buffer
| API | Description |
|---|---|
| napi_create_buffer | Creates a JS Buffer of the specified size. |
| napi_create_buffer_copy | Creates a JS Buffer of the specified size and initializes it with the given data. |
| napi_create_external_buffer | Creates a JS Buffer of the specified size and initializes it with the given data. |
| napi_get_buffer_info | Obtains the underlying data of a JS Buffer and its length. |
| napi_is_buffer | Checks whether the given JS value is a Buffer object. |
| napi_create_external_arraybuffer | Creates a JS ArrayBuffer with external data. |
String
| API | Description |
|---|---|
| napi_create_string_utf16 | Creates a JS string from a UTF16-encoded C string. |
| napi_get_value_string_utf16 | Obtains the UTF16-encoded string corresponding to the given JS value. |
| napi_create_string_latin1 | Creates a JS string from an ISO-8859-1-encoded C string. |
| napi_create_string_utf8 | Creates a JS string from a UTF8-encoded C string. |
| napi_get_value_string_latin1 | Obtains the ISO-8859-1-encoded string corresponding to the given JS value. |
| napi_get_value_string_utf8 | Obtains the UTF8-encoded string corresponding to the given JS value. |
Date
| API | Description |
|---|---|
| napi_create_date | Creates a JS Date object from C double data. |
| napi_get_date_value | Obtains the C double equivalent of the given JS Date object. |
| napi_is_date | Checks whether the given JS value is a JS Date object. |
ArrayBuffer
| API | Description |
|---|---|
| napi_get_arraybuffer_info | Obtains the underlying data buffer of an ArrayBuffer and its length. |
| napi_is_arraybuffer | Checks whether the given JS value is an ArrayBuffer object. |
| napi_detach_arraybuffer | Detaches the underlying data of the given ArrayBuffer. |
| napi_is_detached_arraybuffer | Checks whether the given ArrayBuffer has been detached. |
| napi_create_arraybuffer | Creates a JS ArrayBuffer object of the specified size. |
Module
| API | Description |
|---|---|
| napi_module_register | Registers a native module. |
Lifecycle Management
| API | Description |
|---|---|
| napi_open_handle_scope | Opens a scope. You can use napi_close_handle_scope to close it. |
| napi_close_handle_scope | Closes the scope passed in. After a scope is closed, all references declared in it are closed. |
| napi_open_escapable_handle_scope | Opens a scope from which one object can be prompted to the outer scope. You can use napi_close_escapable_handle_scope to close it. |
| napi_close_escapable_handle_scope | Closes the escapable handle scope passed in. |
| napi_escape_handle | Promotes the handle to the JS object so that it is valid for the lifetime of the parent scope. |
| napi_create_reference | Creates a reference for an object to extend its lifespan. The caller needs to manage the reference lifespan. |
| napi_delete_reference | Deletes the reference passed in. |
| napi_reference_ref | Increments the reference count passed in and returns the new count. |
| napi_reference_unref | Decrements the reference count passed in and returns the new count. |
| napi_get_reference_value | Obtains the JS object associated with the reference. |
| napi_add_finalizer | Adds a napi_finalize callback, which will be called when the JS object is garbage-collected. |
Promise
| API | Description |
|---|---|
| napi_create_promise | Creates a deferred object and a JS promise. |
| napi_resolve_deferred | Resolves a promise by way of the deferred object associated. |
| napi_reject_deferred | Rejects a promise by way of the deferred object associated. |
| napi_is_promise | Checks whether the given napi_value is a promise object. |
Array
| API | Description |
|---|---|
| napi_create_array | Creates a JS Array. |
| napi_create_array_with_length | Creates a JS Array of the specified length. |
| napi_create_typedarray | Creates a JS TypedArray from an existing ArrayBuffer. |
| napi_create_dataview | Creates a JS DataView from an existing ArrayBuffer. |
| napi_get_array_length | Obtains the length of an array. |
| napi_get_typedarray_info | Obtains the properties of a TypedArray. |
| napi_get_dataview_info | Obtains the properties of a DataView. |
| napi_is_array | Checks whether the given JS value is an Array object. |
| napi_set_element | Sets an element at the specified index of the given Object. |
| napi_get_element | Obtains the element at the specified index of the given Object. |
| napi_has_element | Checks whether the given Object has an element at the specified index. |
| napi_delete_element | Deletes the element at the specified index of the given Object. |
Primitives
| API | Description |
|---|---|
| napi_get_boolean | Obtains a JS Boolean object based on the given C Boolean value. |
| napi_get_global | Obtains the global object. |
| napi_get_null | Obtains the null object. |
| napi_get_undefined | Obtains the undefined object. |
| napi_coerce_to_bool | Forcibly converts a JS value into a JS Boolean value. |
| napi_coerce_to_number | Forcibly converts a JS value into a JS number. |
| napi_coerce_to_object | Forcibly converts a JS value into a JS object. |
| napi_coerce_to_string | Forcibly converts a JS value into a JS string. |
Class
| API | Description |
|---|---|
| napi_get_new_target | Obtains the new.target of the constructor call. |
| napi_define_class | Defines a JS class corresponding to the C++ class. |
| napi_new_instance | Creates an instance based on the given constructor. |
Object
| API | Description |
|---|---|
| napi_get_prototype | Obtains the prototype of a JS object. |
| napi_create_object | Creates a default JS object. |
| napi_object_freeze | Freezes an object. |
| napi_object_seal | Seals an object. |
| napi_typeof | Obtains the JS type of a JS value. |
| napi_instanceof | Checks whether the given object is an instance of the specified constructor. |
| napi_type_tag_object | Associates the value of the tag pointer with a JS object. |
| napi_check_object_type_tag | Checks whether a tag pointer is associated with a JS object. |
BigInt
| API | Description |
|---|---|
| napi_create_bigint_int64 | Creates a JS BigInt from C int64 data. |
| napi_create_bigint_uint64 | Creates a JS BigInt from C uint64 data. |
| napi_create_bigint_words | Creates a single JS BigInt from a C uint64 array. |
| napi_get_value_bigint_int64 | Obtains the C int64 equivalent of a JS BigInt. |
| napi_get_value_bigint_uint64 | Obtains the C uint64 equivalent of a JS BigInt. |
| napi_get_value_bigint_words | Obtains information from a JS BigInt, including the sign bit, 64-bit little-endian array, and number of elements in the array. |
Exceptions and Errors
| API | Description |
|---|---|
| napi_throw | Throws a JS value. |
| napi_throw_type_error | Throws a JS type error with text information. |
| napi_throw_range_error | Throws a JS range error with text information. |
| napi_is_error | Checks whether napi_value indicates an error object. |
| napi_create_error | Creates a JS Error with text information. |
| napi_create_type_error | Creates a JS TypeError with text information. |
| napi_create_range_error | Creates a JS RangeError with text information. |
| napi_get_and_clear_last_exception | Obtains and clears the latest exception. |
| napi_is_exception_pending | Checks whether an exception occurs. |
| napi_fatal_error | Raises a fatal error to terminate the process immediately. |
| napi_get_last_error_info | Obtains the napi_extended_error_info struct, which contains the latest error information. |
Property
| API | Description |
|---|---|
| napi_get_property_names | Obtains the names of the enumerable properties of an object in an array of strings. |
| napi_set_property | Sets a property for an object. |
| napi_get_property | Obtains the requested property of an object. |
| napi_has_property | Checks whether an object has the specified property. |
| napi_delete_property | Deletes a property from an object. |
| napi_has_own_property | Checks whether an object has the own property specified by key. |
| napi_set_named_property | Sets a property with the specified name for an object. |
| napi_get_named_property | Obtains the property with the specified name in an object. |
| napi_has_named_property | Checks whether an object has the property with the specified name. |
| napi_define_properties | Defines multiple properties for an object. |
| napi_get_all_property_names | Obtains an array containing the names of all the available properties of this object. |
Async Works
| API | Description |
|---|---|
| napi_create_async_work | Creates a work object that executes logic asynchronously. |
| napi_delete_async_work | Releases an async work object. |
| napi_queue_async_work | Adds an async work object to the queue so that it can be scheduled for execution. |
| napi_cancel_async_work | Cancels a queued async work if it has not been started. |
Custom Async Operations
| API | Description |
|---|---|
| napi_async_init | Creates an async context. The capabilities related to async_hook are not supported. |
| napi_make_callback | Allows a JS function to be called in the async context. The capabilities related to async_hook are not supported. |
| napi_async_destroy | Destroys the previously created async context. The capabilities related to async_hook are not supported. |
| napi_open_callback_scope | Opens a callback scope. The capabilities related to async_hook are not supported. |
| napi_close_callback_scope | Closes the callback scope. The capabilities related to async_hook are not supported. |
Comparing JS Values
| API | Description |
|---|---|
| napi_strict_equals | Checks whether two JS values are strictly equal. |
UV
| API | Description |
|---|---|
| napi_get_uv_event_loop | Obtains the current libuv loop instance. |
Function Invocation
| API | Description |
|---|---|
| napi_call_function | Calls a JS function from a C/C++ addon. |
| napi_get_cb_info | Obtains detailed information about the call, such as the parameters and this pointer, from the given callback info. |
Extension
| API | Description |
|---|---|
| napi_queue_async_work_with_qos | Adds an async work object to the queue and schedules it based on the QoS passed in. |
| napi_run_script_path | Runs an .abc file. |
| napi_load_module | Loads an .abc file as a module. This API returns the namespace of the module. |
| napi_create_object_with_properties | Creates a JS object using the given napi_property_descriptor. The key of the descriptor must be a string and cannot be converted into a number. |
| napi_create_object_with_named_properties | Creates a JS object using the given napi_value and key. The key must be a string and cannot be converted into a number. |
| napi_coerce_to_native_binding_object | Forcibly binds a JS object and a native object. |
napi_queue_async_work_with_qos
napi_status napi_queue_async_work_with_qos(napi_env env,
napi_async_work work,
napi_qos_t qos);
This API has the same usage as napi_queue_async_work. The difference is you can specify the QoS for the work to run.
napi_run_script_path
napi_status napi_run_script_path(napi_env env,
const char* abcPath,
napi_value* result);
napi_load_module
napi_status napi_load_module(napi_env env,
const char* path,
napi_value* result);
napi_create_object_with_properties
napi_status napi_create_object_with_properties(napi_env env,
napi_value* result,
size_t property_count,
const napi_property_descriptor* properties);
napi_create_object_with_named_properties
napi_status napi_create_object_with_named_properties(napi_env env,
napi_value* result,
size_t property_count,
const char** keys,
const napi_value* values);
napi_coerce_to_native_binding_object
napi_status napi_coerce_to_native_binding_object(napi_env env,
napi_value js_object,
napi_native_binding_detach_callback detach_cb,
napi_native_binding_attach_callback attach_cb,
void* native_object,
void* hint);
Environment Lifecycle
| API | Description |
|---|---|
| napi_set_instance_data | Associates data with the currently running environment. |
| napi_get_instance_data | Retrieves the data that was previously associated with the currently running environment. |
Object Lifetime Management
| API | Description |
|---|---|
| napi_add_env_cleanup_hook | Adds a cleanup hook function for releasing resources when the environment exits. |
| napi_remove_env_cleanup_hook | Removes a cleanup hook function. |
| napi_add_async_cleanup_hook | Adds an async cleanup hook function for releasing resources when the environment exits. |
| napi_remove_async_cleanup_hook | Removes an async cleanup hook function. |
Other Utilities
| API | Description |
|---|---|
| node_api_get_module_file_name | Obtains the absolute path of the module to be loaded. |