diff --git a/doc/class_property_descriptor.md b/doc/class_property_descriptor.md index cca90d186..5df283491 100644 --- a/doc/class_property_descriptor.md +++ b/doc/class_property_descriptor.md @@ -1,5 +1,36 @@ -# Class propertry and descriptior +# Class propertry and descriptor -You are reading a draft of the next documentation and it's in continuous update so -if you don't find what you need please refer to: -[C++ wrapper classes for the ABI-stable C APIs for Node.js](https://nodejs.github.io/node-addon-api/) +Property descriptor for use with `Napi::ObjectWrap::DefineClass()`. +This is different from the standalone `Napi::PropertyDescriptor` because it is +specific to each `Napi::ObjectWrap` subclass. +This prevents using descriptors from a different class when defining a new class +(preventing the callbacks from having incorrect `this` pointers). + +## Methods + +### Contructor + +Creates new instance of `Napi::ClassPropertyDescriptor` descriptor object. + +```cpp +Napi::ClassPropertyDescriptor(napi_property_descriptor desc) : _desc(desc) {} +``` + +- `[in] desc`: The `napi_property_descriptor` + +Returns new instance of `Napi::ClassPropertyDescriptor` that is used as property descriptor +inside the `Napi::ObjectWrap` class. + +### Operator + +```cpp +operator napi_property_descriptor&() { return _desc; } +``` + +Returns the original N-API `napi_property_descriptor` wrapped inside the `Napi::ClassPropertyDescriptor` + +```cpp +operator const napi_property_descriptor&() const { return _desc; } +``` + +Returns the original N-API `napi_property_descriptor` wrapped inside the `Napi::ClassPropertyDescriptor` \ No newline at end of file diff --git a/doc/object_wrap.md b/doc/object_wrap.md index 9f4422e61..d422b4e8e 100644 --- a/doc/object_wrap.md +++ b/doc/object_wrap.md @@ -1,13 +1,413 @@ -## Object Wrap - -The ```ObjectWrap``` class can be used to expose C++ code to JavaScript. To do -this you need to extend the ObjectWrap class that contain all the plumbing to connect -JavaScript code to a C++ object. -Classes extending ```ObjectWrap``` can be instantiated from JavaScript using the -**new** operator, and their methods can be directly invoked from JavaScript. -The **wrap** word refers to a way to group methods and state of your class because it -will be your responsibility write custom code to bridge each of your C++ class methods. - -You are reading a draft of the next documentation and it's in continuous update so -if you don't find what you need please refer to: -[C++ wrapper classes for the ABI-stable C APIs for Node.js](https://nodejs.github.io/node-addon-api/) +# Object Wrap + +The `Napi::ObjectWrap` class is used to bind the lifetime of C++ code to a +JavaScript object. Once bound, each time an instance of the JavaScript object +is created, an instance of the C++ class will also be created. When a method +is called on the JavaScript object which is defined as an InstanceMethod, the +corresponding C++ method on the wrapped C++ class will be invoked. + +In order to create a wrapper it's necessary to extend the +`Napi::ObjectWrap`class which contains all the plumbing to connect JavaScript code +with a C++ object. Classes extending `Napi::ObjectWrap` can be instantiated from +JavaScript using the **new** operator, and their methods can be directly invoked +from JavaScript. The **wrap** word refers to a way of grouping methods and state +of the class because it will be necessary write custom code to bridge each of +your C++ class methods. + +## Example + +```cpp +#include + +class Example : public Napi::ObjectWrap { + public: + static Napi::Object Init(Napi::Env env, Napi::Object exports); + Example(const Napi::CallbackInfo &info); + + private: + static Napi::FunctionReference constructor; + double _value; + Napi::Value GetValue(const Napi::CallbackInfo &info); + Napi::Value SetValue(const Napi::CallbackInfo &info); +}; + +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("GetValue", &Example::GetValue), + InstanceMethod("SetValue", &Example::SetValue) + }); + + // Create a peristent 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); + // Call the SuppressDestruct() method on the static data prevent the calling + // to this destructor to reset the reference when the environment is no longer + // available. + constructor.SuppressDestruct(); + exports.Set("Example", func); + return exports; +} + +Example::Example(const Napi::CallbackInfo &info) : Napi::ObjectWrap(info) { + Napi::Env env = info.Env(); + // ... + Napi::Number value = info[0].As(); + this->_value = value.DoubleValue(); +} + +Napi::FunctionReference Example::constructor; + +Napi::Value Example::GetValue(const Napi::CallbackInfo &info){ + Napi::Env env = info.Env(); + return Napi::Number::New(env, this->_value); +} + +Napi::Value Example::SetValue(const Napi::CallbackInfo &info){ + Napi::Env env = info.Env(); + // ... + Napi::Number value = info[0].As(); + this->_value = value.DoubleValue(); + return this->GetValue(info); +} + +// Initialize native add-on +Napi::Object Init (Napi::Env env, Napi::Object exports) { + Example::Init(env, exports); + return exports; +} + +// Regisgter 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 + +### Contructor + +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 instace 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& 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 propertry 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& 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 propertry 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. + +### 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. + +### 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. + +### InstanceMethod + +Creates property descriptor that represents an instance method of a JavaScript class. + +```cpp +static Napi::PropertyDescriptor Napi::ObjectWrap::InstanceMethod(const char* utf8name, + InstanceVoidMethodCallback method, + napi_property_attributes attributes = napi_default, + void* data = nullptr); +``` + +- `[in] utf8name`: Null-terminated string that represents the name of an instance +method for the class. +- `[in] method`: The native function that represents an instance 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 an instance method of a +JavaScript class. + +### InstanceMethod + +Creates property descriptor that represents an instance method of a JavaScript class. + +```cpp +static Napi::PropertyDescriptor Napi::ObjectWrap::InstanceMethod(const char* utf8name, + InstanceMethodCallback method, + napi_property_attributes attributes = napi_default, + void* data = nullptr); +``` + +- `[in] utf8name`: Null-terminated string that represents the name of an instance +method for the class. +- `[in] method`: The native function that represents an instance 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 an instance method of a +JavaScript class. + +### InstanceMethod + +Creates property descriptor that represents an instance method of a JavaScript class. + +```cpp +static Napi::PropertyDescriptor Napi::ObjectWrap::InstanceMethod(Napi::Symbol name, + InstanceVoidMethodCallback method, + napi_property_attributes attributes = napi_default, + void* data = nullptr); +``` + +- `[in] name`: The `Napi::Symbol` object whose value is used to identify the +instance method for the class. +- `[in] method`: The native function that represents an instance 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 an instance method of a +JavaScript class. + +### InstanceMethod + +Creates property descriptor that represents an instance method of a JavaScript class. + +```cpp +static Napi::PropertyDescriptor Napi::ObjectWrap::InstanceMethod(Napi::Symbol name, + InstanceMethodCallback method, + napi_property_attributes attributes = napi_default, + void* data = nullptr); +``` + +- `[in] name`: The `Napi::Symbol` object whose value is used to identify the +instance method for the class. +- `[in] method`: The native function that represents an instance 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 an instance method of a +JavaScript class. + +### InstanceAccessor + +Creates property descriptor that represents an instance accessor property of a +JavaScript class. + +```cpp +static Napi::PropertyDescriptor Napi::ObjectWrap::InstanceAccessor(const char* utf8name, + InstanceGetterCallback getter, + InstanceSetterCallback setter, + napi_property_attributes attributes = napi_default, + void* data = nullptr); +``` + +- `[in] utf8name`: Null-terminated string that represents the name of an instance +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 the particular property. +One or more of `napi_property_attributes`. +- `[in] data`: User-provided data passed into getter or setter when this is invoked. + +Returns `Napi::PropertyDescriptor` object that represents an instance 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 + +### InstanceValue + +Creates property descriptor that represents an instance value property of a +JavaScript class. +```cpp +static Napi::PropertyDescriptor Napi::ObjectWrap::InstanceValue(const char* utf8name, + Napi::Value value, + napi_property_attributes attributes = napi_default); +``` + +- `[in] utf8name`: Null-terminated string that represents the name of the 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. +One or more of `napi_property_attributes`. + +Returns `Napi::PropertyDescriptor` object that represents an instance value +property of a JavaScript class.