addon-tools-el/include/class-wrapping.md

Es5 class wrapping

This wrapping implementation diverges from standard ES6 style wrapping. It also uses composition rather than inheritance, so it is easily pluggable.

• For NAPI addons, super() can be called from C++ side.
• Constructor is callable with ClassName.call(obj, ...args).
• Multiple C++ objects can be attached to a single JS object if it is necessary in an inheritance scenario.
• On JS side util.inherits is used, and on C++ side there is inheritEs5 function.

Class Declaration

class ClassName {
DECLARE_ES5_CLASS(ClassName, JSClassName);
	
public:
	static void init(Napi::Env env, Napi::Object exports);
	explicit ClassName(const Napi::CallbackInfo& info);
	~ClassName();
	
	void _destroy();
	
 private:
	JS_DECLARE_GETTER(ClassName, isDestroyed);
	
	JS_DECLARE_METHOD(ClassName, ClassName, destroy);
	
	bool _isDestroyed;
};

• DECLARE_ES5_CLASS - adds utility declarations, the first argument must be this class name, and the second argument will become the name (arbitrary) of this function (constructor) in JS.
• init - can be used to initialize this class and export it.
• JS_DECLARE_METHOD - declares a method, the first argument is this class, the second is the name of the method to be created.
• JS_DECLARE_GETTER - declares a getter, the first argument is this class, the second is the name of the getter to be created.
• JS_DECLARE_SETTER - declares a setter, the first argument is this class, the second is the name of the setter to be created.

Class Implementation

IMPLEMENT_ES5_CLASS(ClassName);

// Fill the properties and export the class
void ClassName::init(Napi::Env env, Napi::Object exports) {
	Napi::Function ctor = wrap(env);
	JS_ASSIGN_METHOD(destroy);
	JS_ASSIGN_GETTER(isDestroyed);
	// ...
	exports.Set("JSClassName", ctor);
}

ClassName::ClassName(const Napi::CallbackInfo &info) { NAPI_ENV;
	super(info);
	_isDestroyed = false;
	
	// ...
}

ClassName::~ClassName() {
	_destroy();
}

void ClassName::_destroy() { DES_CHECK;
	// ...
	_isDestroyed = true;
}


JS_IMPLEMENT_METHOD(ClassName, destroy) { THIS_CHECK;
	emit("destroy");
	_destroy();
	RET_UNDEFINED;
}


JS_IMPLEMENT_GETTER(ClassName, isDestroyed) { THIS_CHECK;
	RET_BOOL(_isDestroyed);
}

• IMPLEMENT_ES5_CLASS - implements some utility functions for class wrapping.
• JS_ASSIGN_METHOD - in init(), assigns the given method to this class.
• JS_ASSIGN_GETTER - in init(), assigns the given getter to this class.
• JS_ASSIGN_SETTER - in init(), assigns both getter and setter to this class. It also takes only one argument because both have the same name.
• JS_IMPLEMENT_METHOD - implements a method, the first argument is this class, the second is the name of the method being implemented.
• JS_IMPLEMENT_GETTER - implements a getter, the first argument is this class, the second is the name of the getter being implemented.
• JS_IMPLEMENT_SETTER - implements a setter, the first argument is this class, the second is the name of the setter being implemented.