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295 lines
9.4 KiB
Markdown
295 lines
9.4 KiB
Markdown
# Function
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The `Napi::Function` class provides a set of methods for creating a function object in
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native code that can later be called from JavaScript. The created function is not
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automatically visible from JavaScript. Instead it needs to be part of the add-on's
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module exports or be returned by one of the module's exported functions.
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In addition the `Napi::Function` class also provides methods that can be used to call
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functions that were created in JavaScript and passed to the native add-on.
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The `Napi::Function` class inherits its behavior from the `Napi::Object` class (for more info
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see: [`Napi::Object`](object.md)).
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## Example
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```cpp
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#include <napi.h>
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using namespace Napi;
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Value Fn(const CallbackInfo& info) {
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Env env = info.Env();
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// ...
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return String::New(env, "Hello World");
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}
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Object Init(Env env, Object exports) {
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exports.Set(String::New(env, "fn"), Function::New(env, Fn));
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}
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NODE_API_MODULE(NODE_GYP_MODULE_NAME, Init)
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```
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The above code can be used from JavaScript as follows:
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```js
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const addon = require('./addon');
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addon.fn();
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```
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With the `Napi::Function` class it is possible to call a JavaScript function object
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from a native add-on with two different methods: `Call` and `MakeCallback`.
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The API of these two methods is very similar, but they are used in different
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contexts. The `MakeCallback` method is used to call from native code back into
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JavaScript after returning from an [asynchronous operation](async_operations.md)
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and in general in situations which don't have an existing JavaScript function on
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the stack. The `Call` method is used when there is already a JavaScript function
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on the stack (for example when running a native method called from JavaScript).
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## Methods
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### Constructor
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Creates a new empty instance of `Napi::Function`.
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```cpp
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Napi::Function::Function();
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```
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### Constructor
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Creates a new instance of the `Napi::Function` object.
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```cpp
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Napi::Function::Function(napi_env env, napi_value value);
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```
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- `[in] env`: The `napi_env` environment in which to construct the `Napi::Function` object.
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- `[in] value`: The `napi_value` which is a handle for a JavaScript function.
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Returns a non-empty `Napi::Function` instance.
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### New
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Creates an instance of a `Napi::Function` object.
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```cpp
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template <typename Callable>
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static Napi::Function Napi::Function::New(napi_env env, Callable cb, const char* utf8name = nullptr, void* data = nullptr);
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```
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- `[in] env`: The `napi_env` environment in which to construct the `Napi::Function` object.
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- `[in] cb`: Object that implements `Callable`.
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- `[in] utf8name`: Null-terminated string to be used as the name of the function.
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- `[in] data`: User-provided data context. This will be passed back into the
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function when invoked later.
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Returns an instance of a `Napi::Function` object.
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### New
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```cpp
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template <typename Callable>
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static Napi::Function Napi::Function::New(napi_env env, Callable cb, const std::string& utf8name, void* data = nullptr);
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```
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- `[in] env`: The `napi_env` environment in which to construct the `Napi::Function` object.
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- `[in] cb`: Object that implements `Callable`.
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- `[in] utf8name`: String to be used as the name of the function.
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- `[in] data`: User-provided data context. This will be passed back into the
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function when invoked later.
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Returns an instance of a `Napi::Function` object.
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### New
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Creates a new JavaScript value from one that represents the constructor for the
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object.
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```cpp
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Napi::Object Napi::Function::New(const std::initializer_list<napi_value>& args) const;
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```
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- `[in] args`: Initializer list of JavaScript values as `napi_value` representing
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the arguments of the contructor function.
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Returns a new JavaScript object.
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### New
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Creates a new JavaScript value from one that represents the constructor for the
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object.
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```cpp
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Napi::Object Napi::Function::New(const std::vector<napi_value>& args) const;
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```
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- `[in] args`: Vector of JavaScript values as `napi_value` representing the
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arguments of the constructor function.
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Returns a new JavaScript object.
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### New
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Creates a new JavaScript value from one that represents the constructor for the
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object.
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```cpp
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Napi::Object Napi::Function::New(size_t argc, const napi_value* args) const;
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```
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- `[in] argc`: The number of the arguments passed to the contructor function.
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- `[in] args`: Array of JavaScript values as `napi_value` representing the
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arguments of the constructor function.
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Returns a new JavaScript object.
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### Call
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Calls a Javascript function from a native add-on.
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```cpp
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Napi::Value Napi::Function::Call(const std::initializer_list<napi_value>& args) const;
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```
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- `[in] args`: Initializer list of JavaScript values as `napi_value` representing
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the arguments of the function.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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### Call
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Calls a JavaScript function from a native add-on.
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```cpp
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Napi::Value Napi::Function::Call(const std::vector<napi_value>& args) const;
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```
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- `[in] args`: Vector of JavaScript values as `napi_value` representing the
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arguments of the function.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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### Call
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Calls a Javascript function from a native add-on.
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```cpp
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Napi::Value Napi::Function::Call(size_t argc, const napi_value* args) const;
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```
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- `[in] argc`: The number of the arguments passed to the function.
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- `[in] args`: Array of JavaScript values as `napi_value` representing the
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arguments of the function.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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### Call
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Calls a Javascript function from a native add-on.
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```cpp
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Napi::Value Napi::Function::Call(napi_value recv, const std::initializer_list<napi_value>& args) const;
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```
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- `[in] recv`: The `this` object passed to the called function.
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- `[in] args`: Initializer list of JavaScript values as `napi_value` representing
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the arguments of the function.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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### Call
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Calls a Javascript function from a native add-on.
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```cpp
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Napi::Value Napi::Function::Call(napi_value recv, const std::vector<napi_value>& args) const;
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```
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- `[in] recv`: The `this` object passed to the called function.
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- `[in] args`: Vector of JavaScript values as `napi_value` representing the
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arguments of the function.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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### Call
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Calls a Javascript function from a native add-on.
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```cpp
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Napi::Value Napi::Function::Call(napi_value recv, size_t argc, const napi_value* args) const;
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```
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- `[in] recv`: The `this` object passed to the called function.
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- `[in] argc`: The number of the arguments passed to the function.
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- `[in] args`: Array of JavaScript values as `napi_value` representing the
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arguments of the function.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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### MakeCallback
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Calls a Javascript function from a native add-on after an asynchronous operation.
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```cpp
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Napi::Value Napi::Function::MakeCallback(napi_value recv, const std::initializer_list<napi_value>& args, napi_async_context context = nullptr) const;
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```
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- `[in] recv`: The `this` object passed to the called function.
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- `[in] args`: Initializer list of JavaScript values as `napi_value` representing
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the arguments of the function.
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- `[in] context`: Context for the async operation that is invoking the callback.
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This should normally be a value previously obtained from [Napi::AsyncContext](async_context.md).
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However `nullptr` is also allowed, which indicates the current async context
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(if any) is to be used for the callback.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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### MakeCallback
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Calls a Javascript function from a native add-on after an asynchronous operation.
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```cpp
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Napi::Value Napi::Function::MakeCallback(napi_value recv, const std::vector<napi_value>& args, napi_async_context context = nullptr) const;
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```
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- `[in] recv`: The `this` object passed to the called function.
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- `[in] args`: List of JavaScript values as `napi_value` representing the
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arguments of the function.
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- `[in] context`: Context for the async operation that is invoking the callback.
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This should normally be a value previously obtained from [Napi::AsyncContext](async_context.md).
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However `nullptr` is also allowed, which indicates the current async context
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(if any) is to be used for the callback.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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### MakeCallback
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Calls a Javascript function from a native add-on after an asynchronous operation.
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```cpp
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Napi::Value Napi::Function::MakeCallback(napi_value recv, size_t argc, const napi_value* args, napi_async_context context = nullptr) const;
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```
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- `[in] recv`: The `this` object passed to the called function.
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- `[in] argc`: The number of the arguments passed to the function.
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- `[in] args`: Array of JavaScript values as `napi_value` representing the
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arguments of the function.
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- `[in] context`: Context for the async operation that is invoking the callback.
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This should normally be a value previously obtained from [Napi::AsyncContext](async_context.md).
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However `nullptr` is also allowed, which indicates the current async context
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(if any) is to be used for the callback.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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## Operator
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```cpp
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Napi::Value Napi::Function::operator ()(const std::initializer_list<napi_value>& args) const;
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```
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- `[in] args`: Initializer list of JavaScript values as `napi_value`.
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Returns a `Napi::Value` representing the JavaScript value returned by the function.
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