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node_modules/node-addon-api/doc/object_wrap.md
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node_modules/node-addon-api/doc/object_wrap.md
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# Object Wrap
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Class `Napi::ObjectWrap<T>` inherits from class [`Napi::InstanceWrap<T>`][].
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|
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The `Napi::ObjectWrap<T>` class is used to bind the lifetime of C++ code to a
|
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JavaScript object. Once bound, each time an instance of the JavaScript object
|
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is created, an instance of the C++ class will also be created. When a method
|
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is called on the JavaScript object which is defined as an InstanceMethod, the
|
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corresponding C++ method on the wrapped C++ class will be invoked.
|
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|
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In order to create a wrapper it's necessary to extend the
|
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`Napi::ObjectWrap<T>` class which contains all the plumbing to connect
|
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JavaScript code with a C++ object. Classes extending `Napi::ObjectWrap` can be
|
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instantiated from JavaScript using the **new** operator, and their methods can
|
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be directly invoked from JavaScript. The **wrap** word refers to a way of
|
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grouping methods and state of the class because it will be necessary write
|
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custom code to bridge each of your C++ class methods.
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|
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## Example
|
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|
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```cpp
|
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#include <napi.h>
|
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|
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class Example : public Napi::ObjectWrap<Example> {
|
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public:
|
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static Napi::Object Init(Napi::Env env, Napi::Object exports);
|
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Example(const Napi::CallbackInfo& info);
|
||||
static Napi::Value CreateNewItem(const Napi::CallbackInfo& info);
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|
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private:
|
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double _value;
|
||||
Napi::Value GetValue(const Napi::CallbackInfo& info);
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Napi::Value SetValue(const Napi::CallbackInfo& info);
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};
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|
||||
Napi::Object Example::Init(Napi::Env env, Napi::Object exports) {
|
||||
// This method is used to hook the accessor and method callbacks
|
||||
Napi::Function func = DefineClass(env, "Example", {
|
||||
InstanceMethod<&Example::GetValue>("GetValue"),
|
||||
InstanceMethod<&Example::SetValue>("SetValue"),
|
||||
StaticMethod<&Example::CreateNewItem>("CreateNewItem"),
|
||||
});
|
||||
|
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Napi::FunctionReference* constructor = new Napi::FunctionReference();
|
||||
|
||||
// Create a persistent reference to the class constructor. This will allow
|
||||
// a function called on a class prototype and a function
|
||||
// called on instance of a class to be distinguished from each other.
|
||||
*constructor = Napi::Persistent(func);
|
||||
exports.Set("Example", func);
|
||||
|
||||
// Store the constructor as the add-on instance data. This will allow this
|
||||
// add-on to support multiple instances of itself running on multiple worker
|
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// threads, as well as multiple instances of itself running in different
|
||||
// contexts on the same thread.
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//
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// By default, the value set on the environment here will be destroyed when
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||||
// the add-on is unloaded using the `delete` operator, but it is also
|
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// possible to supply a custom deleter.
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env.SetInstanceData<Napi::FunctionReference>(constructor);
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return exports;
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}
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|
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Example::Example(const Napi::CallbackInfo& info) :
|
||||
Napi::ObjectWrap<Example>(info) {
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Napi::Env env = info.Env();
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// ...
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||||
Napi::Number value = info[0].As<Napi::Number>();
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||||
this->_value = value.DoubleValue();
|
||||
}
|
||||
|
||||
Napi::Value Example::GetValue(const Napi::CallbackInfo& info){
|
||||
Napi::Env env = info.Env();
|
||||
return Napi::Number::New(env, this->_value);
|
||||
}
|
||||
|
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Napi::Value Example::SetValue(const Napi::CallbackInfo& info){
|
||||
Napi::Env env = info.Env();
|
||||
// ...
|
||||
Napi::Number value = info[0].As<Napi::Number>();
|
||||
this->_value = value.DoubleValue();
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||||
return this->GetValue(info);
|
||||
}
|
||||
|
||||
// Initialize native add-on
|
||||
Napi::Object Init (Napi::Env env, Napi::Object exports) {
|
||||
Example::Init(env, exports);
|
||||
return exports;
|
||||
}
|
||||
|
||||
// Create a new item using the constructor stored during Init.
|
||||
Napi::Value Example::CreateNewItem(const Napi::CallbackInfo& info) {
|
||||
// Retrieve the instance data we stored during `Init()`. We only stored the
|
||||
// constructor there, so we retrieve it here to create a new instance of the
|
||||
// JS class the constructor represents.
|
||||
Napi::FunctionReference* constructor =
|
||||
info.Env().GetInstanceData<Napi::FunctionReference>();
|
||||
return constructor->New({ Napi::Number::New(info.Env(), 42) });
|
||||
}
|
||||
|
||||
// Register and initialize native add-on
|
||||
NODE_API_MODULE(NODE_GYP_MODULE_NAME, Init)
|
||||
```
|
||||
|
||||
The above code can be used from JavaScript as follows:
|
||||
|
||||
```js
|
||||
'use strict'
|
||||
|
||||
const { Example } = require('bindings')('addon')
|
||||
|
||||
const example = new Example(11)
|
||||
console.log(example.GetValue())
|
||||
// It prints 11
|
||||
example.SetValue(19)
|
||||
console.log(example.GetValue());
|
||||
// It prints 19
|
||||
```
|
||||
|
||||
At initialization time, the `Napi::ObjectWrap::DefineClass()` method must be
|
||||
used to hook up the accessor and method callbacks. It takes a list of property
|
||||
descriptors, which can be constructed via the various static methods on the base
|
||||
class.
|
||||
|
||||
When JavaScript code invokes the constructor, the constructor callback will
|
||||
create a new C++ instance and "wrap" it into the newly created JavaScript
|
||||
object.
|
||||
|
||||
When JavaScript code invokes a method or a property accessor on the class the
|
||||
corresponding C++ callback function will be executed.
|
||||
|
||||
For a wrapped object it could be difficult to distinguish between a function
|
||||
called on a class prototype and a function called on instance of a class.
|
||||
Therefore it is good practice to save a persistent reference to the class
|
||||
constructor. This allows the two cases to be distinguished from each other by
|
||||
checking the this object against the class constructor.
|
||||
|
||||
## Methods
|
||||
|
||||
### Constructor
|
||||
|
||||
Creates a new instance of a JavaScript object that wraps native instance.
|
||||
|
||||
```cpp
|
||||
Napi::ObjectWrap(const Napi::CallbackInfo& callbackInfo);
|
||||
```
|
||||
|
||||
- `[in] callbackInfo`: The object representing the components of the JavaScript
|
||||
request being made.
|
||||
|
||||
### Unwrap
|
||||
|
||||
Retrieves a native instance wrapped in a JavaScript object.
|
||||
|
||||
```cpp
|
||||
static T* Napi::ObjectWrap::Unwrap(Napi::Object wrapper);
|
||||
```
|
||||
|
||||
* `[in] wrapper`: The JavaScript object that wraps the native instance.
|
||||
|
||||
Returns a native instance wrapped in a JavaScript object. Given the
|
||||
Napi:Object, this allows a method to get a pointer to the wrapped
|
||||
C++ object and then reference fields, call methods, etc. within that class.
|
||||
In many cases calling Unwrap is not required, as methods can
|
||||
use the `this` field for ObjectWrap when running in a method on a
|
||||
class that extends ObjectWrap.
|
||||
|
||||
### DefineClass
|
||||
|
||||
Defnines a JavaScript class with constructor, static and instance properties and
|
||||
methods.
|
||||
|
||||
```cpp
|
||||
static Napi::Function Napi::ObjectWrap::DefineClass(Napi::Env env,
|
||||
const char* utf8name,
|
||||
const std::initializer_list<PropertyDescriptor>& properties,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
* `[in] env`: The environment in which to construct a JavaScript class.
|
||||
* `[in] utf8name`: Null-terminated string that represents the name of the
|
||||
JavaScript constructor function.
|
||||
* `[in] properties`: Initializer list of class property descriptor describing
|
||||
static and instance properties and methods of the class.
|
||||
See: [`Class property and descriptor`](class_property_descriptor.md).
|
||||
* `[in] data`: User-provided data passed to the constructor callback as `data`
|
||||
property of the `Napi::CallbackInfo`.
|
||||
|
||||
Returns a `Napi::Function` representing the constructor function for the class.
|
||||
|
||||
### DefineClass
|
||||
|
||||
Defnines a JavaScript class with constructor, static and instance properties and
|
||||
methods.
|
||||
|
||||
```cpp
|
||||
static Napi::Function Napi::ObjectWrap::DefineClass(Napi::Env env,
|
||||
const char* utf8name,
|
||||
const std::vector<PropertyDescriptor>& properties,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
* `[in] env`: The environment in which to construct a JavaScript class.
|
||||
* `[in] utf8name`: Null-terminated string that represents the name of the
|
||||
JavaScript constructor function.
|
||||
* `[in] properties`: Vector of class property descriptor describing static and
|
||||
instance properties and methods of the class.
|
||||
See: [`Class property and descriptor`](class_property_descriptor.md).
|
||||
* `[in] data`: User-provided data passed to the constructor callback as `data`
|
||||
property of the `Napi::CallbackInfo`.
|
||||
|
||||
Returns a `Napi::Function` representing the constructor function for the class.
|
||||
|
||||
### Finalize
|
||||
|
||||
Provides an opportunity to run cleanup code that requires access to the
|
||||
`Napi::Env` before the wrapped native object instance is freed. Override to
|
||||
implement.
|
||||
|
||||
```cpp
|
||||
virtual void Finalize(Napi::Env env);
|
||||
```
|
||||
|
||||
- `[in] env`: `Napi::Env`.
|
||||
|
||||
### StaticMethod
|
||||
|
||||
Creates property descriptor that represents a static method of a JavaScript
|
||||
class.
|
||||
|
||||
```cpp
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticMethod(
|
||||
const char* utf8name,
|
||||
StaticVoidMethodCallback method,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] utf8name`: Null-terminated string that represents the name of a static
|
||||
method for the class.
|
||||
- `[in] method`: The native function that represents a static method of a
|
||||
JavaScript class.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into method when it is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents the static method of a
|
||||
JavaScript class.
|
||||
|
||||
### StaticMethod
|
||||
|
||||
Creates property descriptor that represents a static method of a JavaScript
|
||||
class.
|
||||
|
||||
```cpp
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticMethod(
|
||||
const char* utf8name,
|
||||
StaticMethodCallback method,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] utf8name`: Null-terminated string that represents the name of a static
|
||||
method for the class.
|
||||
- `[in] method`: The native function that represents a static method of a
|
||||
JavaScript class.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into method when it is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents a static method of a
|
||||
JavaScript class.
|
||||
|
||||
### StaticMethod
|
||||
|
||||
Creates property descriptor that represents a static method of a JavaScript
|
||||
class.
|
||||
|
||||
```cpp
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticMethod(Symbol name,
|
||||
StaticVoidMethodCallback method,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] name`: Napi:Symbol that represents the name of a static
|
||||
method for the class.
|
||||
- `[in] method`: The native function that represents a static method of a
|
||||
JavaScript class.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into method when it is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents the static method of a
|
||||
JavaScript class.
|
||||
|
||||
### StaticMethod
|
||||
|
||||
Creates property descriptor that represents a static method of a JavaScript
|
||||
class.
|
||||
|
||||
```cpp
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticMethod(Symbol name,
|
||||
StaticMethodCallback method,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
method for the class.
|
||||
- `[in] name`: Napi:Symbol that represents the name of a static.
|
||||
- `[in] method`: The native function that represents a static method of a
|
||||
JavaScript class.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into method when it is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents a static method of a
|
||||
JavaScript class.
|
||||
|
||||
### StaticMethod
|
||||
|
||||
Creates property descriptor that represents a static method of a JavaScript
|
||||
class.
|
||||
|
||||
```cpp
|
||||
template <StaticVoidMethodCallback method>
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticMethod(
|
||||
const char* utf8name,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] method`: The native function that represents a static method of a
|
||||
JavaScript class. This function returns nothing.
|
||||
- `[in] utf8name`: Null-terminated string that represents the name of a static
|
||||
method for the class.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into method when it is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents the static method of a
|
||||
JavaScript class.
|
||||
|
||||
### StaticMethod
|
||||
|
||||
Creates property descriptor that represents a static method of a JavaScript
|
||||
class.
|
||||
|
||||
```cpp
|
||||
template <StaticMethodCallback method>
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticMethod(
|
||||
const char* utf8name,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] method`: The native function that represents a static method of a
|
||||
JavaScript class.
|
||||
- `[in] utf8name`: Null-terminated string that represents the name of a static
|
||||
method for the class.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into method when it is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents a static method of a
|
||||
JavaScript class.
|
||||
|
||||
### StaticMethod
|
||||
|
||||
Creates property descriptor that represents a static method of a JavaScript
|
||||
class.
|
||||
|
||||
```cpp
|
||||
template <StaticVoidMethodCallback method>
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticMethod(Symbol name,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] method`: The native function that represents a static method of a
|
||||
JavaScript class.
|
||||
- `[in] name`: Napi:Symbol that represents the name of a static
|
||||
method for the class.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into method when it is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents the static method of a
|
||||
JavaScript class.
|
||||
|
||||
### StaticMethod
|
||||
|
||||
Creates property descriptor that represents a static method of a JavaScript
|
||||
class.
|
||||
|
||||
```cpp
|
||||
template <StaticMethodCallback method>
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticMethod(Symbol name,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] method`: The native function that represents a static method of a
|
||||
JavaScript class.
|
||||
- `[in] name`: Napi:Symbol that represents the name of a static.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into method when it is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents a static method of a
|
||||
JavaScript class.
|
||||
|
||||
### StaticAccessor
|
||||
|
||||
Creates property descriptor that represents a static accessor property of a
|
||||
JavaScript class.
|
||||
|
||||
```cpp
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticAccessor(
|
||||
const char* utf8name,
|
||||
StaticGetterCallback getter,
|
||||
StaticSetterCallback setter,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] utf8name`: Null-terminated string that represents the name of a static
|
||||
accessor property for the class.
|
||||
- `[in] getter`: The native function to call when a get access to the property
|
||||
of a JavaScript class is performed.
|
||||
- `[in] setter`: The native function to call when a set access to the property
|
||||
of a JavaScript class is performed.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into getter or setter when
|
||||
is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents a static accessor
|
||||
property of a JavaScript class.
|
||||
|
||||
### StaticAccessor
|
||||
|
||||
Creates property descriptor that represents a static accessor property of a
|
||||
JavaScript class.
|
||||
|
||||
```cpp
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticAccessor(Symbol name,
|
||||
StaticGetterCallback getter,
|
||||
StaticSetterCallback setter,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] name`: Napi:Symbol that represents the name of a static accessor.
|
||||
- `[in] getter`: The native function to call when a get access to the property
|
||||
of a JavaScript class is performed.
|
||||
- `[in] setter`: The native function to call when a set access to the property
|
||||
of a JavaScript class is performed.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into getter or setter when
|
||||
is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents a static accessor
|
||||
property of a JavaScript class.
|
||||
|
||||
### StaticAccessor
|
||||
|
||||
Creates property descriptor that represents a static accessor property of a
|
||||
JavaScript class.
|
||||
|
||||
```cpp
|
||||
template <StaticGetterCallback getter, StaticSetterCallback setter=nullptr>
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticAccessor(
|
||||
const char* utf8name,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] getter`: The native function to call when a get access to the property
|
||||
of a JavaScript class is performed.
|
||||
- `[in] setter`: The native function to call when a set access to the property
|
||||
of a JavaScript class is performed.
|
||||
- `[in] utf8name`: Null-terminated string that represents the name of a static
|
||||
accessor property for the class.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into getter or setter when
|
||||
is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents a static accessor
|
||||
property of a JavaScript class.
|
||||
|
||||
### StaticAccessor
|
||||
|
||||
Creates property descriptor that represents a static accessor property of a
|
||||
JavaScript class.
|
||||
|
||||
```cpp
|
||||
template <StaticGetterCallback getter, StaticSetterCallback setter=nullptr>
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticAccessor(Symbol name,
|
||||
napi_property_attributes attributes = napi_default,
|
||||
void* data = nullptr);
|
||||
```
|
||||
|
||||
- `[in] getter`: The native function to call when a get access to the property
|
||||
of a JavaScript class is performed.
|
||||
- `[in] setter`: The native function to call when a set access to the property
|
||||
of a JavaScript class is performed.
|
||||
- `[in] name`: Napi:Symbol that represents the name of a static accessor.
|
||||
- `[in] attributes`: The attributes associated with a particular property.
|
||||
One or more of `napi_property_attributes`.
|
||||
- `[in] data`: User-provided data passed into getter or setter when
|
||||
is invoked.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents a static accessor
|
||||
property of a JavaScript class.
|
||||
|
||||
### StaticValue
|
||||
|
||||
Creates property descriptor that represents an static value property of a
|
||||
JavaScript class.
|
||||
```cpp
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticValue(
|
||||
const char* utf8name,
|
||||
Napi::Value value,
|
||||
napi_property_attributes attributes = napi_default);
|
||||
```
|
||||
|
||||
- `[in] utf8name`: Null-terminated string that represents the name of the static
|
||||
property.
|
||||
- `[in] value`: The value that's retrieved by a get access of the property.
|
||||
- `[in] attributes`: The attributes to be associated with the property in
|
||||
addition to the napi_static attribute. One or more of
|
||||
`napi_property_attributes`.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents an static value
|
||||
property of a JavaScript class
|
||||
|
||||
### StaticValue
|
||||
|
||||
Creates property descriptor that represents an static value property of a
|
||||
JavaScript class.
|
||||
```cpp
|
||||
static Napi::PropertyDescriptor Napi::ObjectWrap::StaticValue(Symbol name,
|
||||
Napi::Value value,
|
||||
napi_property_attributes attributes = napi_default);
|
||||
```
|
||||
|
||||
- `[in] name`: The `Napi::Symbol` object whose value is used to identify the
|
||||
name of the static property.
|
||||
- `[in] value`: The value that's retrieved by a get access of the property.
|
||||
- `[in] attributes`: The attributes to be associated with the property in
|
||||
addition to the napi_static attribute. One or more of
|
||||
`napi_property_attributes`.
|
||||
|
||||
Returns `Napi::PropertyDescriptor` object that represents an static value
|
||||
property of a JavaScript class
|
||||
|
||||
[`Napi::InstanceWrap<T>`]: ./instance_wrap.md
|
||||
Reference in New Issue
Block a user