# FunctionReference `Napi::FunctionReference` is a subclass of [`Napi::Reference`](reference.md), and is equivalent to an instance of `Napi::Reference`. This means that a `Napi::FunctionReference` holds a [`Napi::Function`](function.md), and a count of the number of references to that `Napi::Function`. When the count is greater than 0, a `Napi::FunctionReference` is not eligible for garbage collection. This ensures that the `Function` will remain accessible, even if the original reference to it is no longer available. `Napi::FunctionReference` allows the referenced JavaScript function object to be called from a native add-on with two different methods: `Call` and `MakeCallback`. See the documentation for [`Napi::Function`](function.md) for when `Call` should be used instead of `MakeCallback` and vice-versa. The `Napi::FunctionReference` class inherits its behavior from the `Napi::Reference` class (for more info see: [`Napi::Reference`](reference.md)). ## Methods ### Weak Creates a "weak" reference to the value, in that the initial reference count is set to 0. ```cpp static Napi::FunctionReference Napi::Weak(const Napi::Function& value); ``` - `[in] value`: The value which is to be referenced. Returns the newly created reference. ### Persistent Creates a "persistent" reference to the value, in that the initial reference count is set to 1. ```cpp static Napi::FunctionReference Napi::Persistent(const Napi::Function& value); ``` - `[in] value`: The value which is to be referenced. Returns the newly created reference. ### Constructor Creates a new empty instance of `Napi::FunctionReference`. ```cpp Napi::FunctionReference::FunctionReference(); ``` ### Constructor Creates a new instance of the `Napi::FunctionReference`. ```cpp Napi::FunctionReference::FunctionReference(napi_env env, napi_ref ref); ``` - `[in] env`: The environment in which to construct the `Napi::FunctionReference` object. - `[in] ref`: The N-API reference to be held by the `Napi::FunctionReference`. Returns a newly created `Napi::FunctionReference` object. ### New Constructs a new instance by calling the constructor held by this reference. ```cpp Napi::Object Napi::FunctionReference::New(const std::initializer_list& args) const; ``` - `[in] args`: Initializer list of JavaScript values as `napi_value` representing the arguments of the contructor function. Returns a new JavaScript object. ### New Constructs a new instance by calling the constructor held by this reference. ```cpp Napi::Object Napi::FunctionReference::New(const std::vector& args) const; ``` - `[in] args`: Vector of JavaScript values as `napi_value` representing the arguments of the constructor function. Returns a new JavaScript object. ### Call Calls a referenced Javascript function from a native add-on. ```cpp Napi::Value Napi::FunctionReference::Call(const std::initializer_list& args) const; ``` - `[in] args`: Initializer list of JavaScript values as `napi_value` representing the arguments of the referenced function. Returns a `Napi::Value` representing the JavaScript object returned by the referenced function. ### Call Calls a referenced JavaScript function from a native add-on. ```cpp Napi::Value Napi::FunctionReference::Call(const std::vector& args) const; ``` - `[in] args`: Vector of JavaScript values as `napi_value` representing the arguments of the referenced function. Returns a `Napi::Value` representing the JavaScript object returned by the referenced function. ### Call Calls a referenced JavaScript function from a native add-on. ```cpp Napi::Value Napi::FunctionReference::Call(napi_value recv, const std::initializer_list& args) const; ``` - `[in] recv`: The `this` object passed to the referenced function when it's called. - `[in] args`: Initializer list of JavaScript values as `napi_value` representing the arguments of the referenced function. Returns a `Napi::Value` representing the JavaScript object returned by the referenced function. ### Call Calls a referenced JavaScript function from a native add-on. ```cpp Napi::Value Napi::FunctionReference::Call(napi_value recv, const std::vector& args) const; ``` - `[in] recv`: The `this` object passed to the referenced function when it's called. - `[in] args`: Vector of JavaScript values as `napi_value` representing the arguments of the referenced function. Returns a `Napi::Value` representing the JavaScript object returned by the referenced function. ### Call Calls a referenced JavaScript function from a native add-on. ```cpp Napi::Value Napi::FunctionReference::Call(napi_value recv, size_t argc, const napi_value* args) const; ``` - `[in] recv`: The `this` object passed to the referenced function when it's called. - `[in] argc`: The number of arguments passed to the referenced function. - `[in] args`: Array of JavaScript values as `napi_value` representing the arguments of the referenced function. Returns a `Napi::Value` representing the JavaScript object returned by the referenced function. ### MakeCallback Calls a referenced JavaScript function from a native add-on after an asynchronous operation. ```cpp Napi::Value Napi::FunctionReference::MakeCallback(napi_value recv, const std::initializer_list& args, napi_async_context = nullptr) const; ``` - `[in] recv`: The `this` object passed to the referenced function when it's called. - `[in] args`: Initializer list of JavaScript values as `napi_value` representing the arguments of the referenced function. - `[in] context`: Context for the async operation that is invoking the callback. This should normally be a value previously obtained from [Napi::AsyncContext](async_context.md). However `nullptr` is also allowed, which indicates the current async context (if any) is to be used for the callback. Returns a `Napi::Value` representing the JavaScript object returned by the referenced function. ### MakeCallback Calls a referenced JavaScript function from a native add-on after an asynchronous operation. ```cpp Napi::Value Napi::FunctionReference::MakeCallback(napi_value recv, const std::vector& args, napi_async_context context = nullptr) const; ``` - `[in] recv`: The `this` object passed to the referenced function when it's called. - `[in] args`: Vector of JavaScript values as `napi_value` representing the arguments of the referenced function. - `[in] context`: Context for the async operation that is invoking the callback. This should normally be a value previously obtained from [Napi::AsyncContext](async_context.md). However `nullptr` is also allowed, which indicates the current async context (if any) is to be used for the callback. Returns a `Napi::Value` representing the JavaScript object returned by the referenced function. ### MakeCallback Calls a referenced JavaScript function from a native add-on after an asynchronous operation. ```cpp Napi::Value Napi::FunctionReference::MakeCallback(napi_value recv, size_t argc, const napi_value* args, napi_async_context context = nullptr) const; ``` - `[in] recv`: The `this` object passed to the referenced function when it's called. - `[in] argc`: The number of arguments passed to the referenced function. - `[in] args`: Array of JavaScript values as `napi_value` representing the arguments of the referenced function. - `[in] context`: Context for the async operation that is invoking the callback. This should normally be a value previously obtained from [Napi::AsyncContext](async_context.md). However `nullptr` is also allowed, which indicates the current async context (if any) is to be used for the callback. Returns a `Napi::Value` representing the JavaScript object returned by the referenced function. ## Operator ```cpp Napi::Value operator ()(const std::initializer_list& args) const; ``` - `[in] args`: Initializer list of reference to JavaScript values as `napi_value` Returns a `Napi::Value` representing the JavaScript value returned by the referenced function.