"make3" implementation

type-declarations.js

/*
 * Forked Zakas' attempt at a `type()` "class" maker/extender utility.
 * This variation just makes and links objects, without the unnecessity
 * of using constructor functions. You can however specify `init()`
 * functions to use upon creation of the object. NOTE: because there are
 * no more constructor functions, comparisons with `instanceof` and
 * `constructor` no longer apply.
 */

function make(delegateTo, declaration) {
	function mixin(receiver, supplier) {
		if (Object.getOwnPropertyDescriptor) {
			Object.keys(supplier).forEach(function(property) {
				var descriptor = Object.getOwnPropertyDescriptor(supplier, property);
				Object.defineProperty(receiver, property, descriptor);
			});
		}
		else {
			for (var property in supplier) {
				if (supplier.hasOwnProperty(property)) {
					receiver[property] = supplier[property]
				}
			}
		}
		return receiver;
	}

	// if `delegateTo` not specified, default: `Object.prototype`
	if (!delegateTo) {
		delegateTo = Object.prototype;
	}

	// make sure the `delegateTo` is an object
	delegateTo = (typeof delegateTo == "function") ? delegateTo.prototype : delegateTo;

	// link the new object to the `delegateTo` object
	var obj = Object.create(delegateTo);

	// define the new object according to the declaration (if any)
	if (declaration) {
		mixin(obj,declaration||{});
	}

	// if no `init` was declared for this new object, but `delegateTo.init()` exists,
	// hook up to it automatically
	if (!obj.hasOwnProperty("init") && delegateTo && delegateTo.hasOwnProperty("init")) {
		obj.init = function(){ return delegateTo.init.apply(this,arguments); };
	}

	return obj;
}

//---------------------------------------------------------------------------
// Usage
//---------------------------------------------------------------------------

var Rectangle = {
	init: function(length, width) {
		this.length = length;
		this.width = width;
	},
	getArea: function() {
		return this.length * this.width;
	}
};

// inherit from rectangle
var Square = make(Rectangle,{
	init: function(size) {
		Rectangle.init.call(this, size, size);
	}
});

// also inherit from rectangle
var Triangle = make(Rectangle,{
	getArea: function() {
		return 0.5 * this.length * this.width;
	}
});

var rect = Object.create(Rectangle);
rect.init.call(rect,3,10);
console.log(Rectangle.isPrototypeOf(rect));     // true
console.log(rect.getArea());                    // 30

var square = Object.create(Square);
square.init.call(square,10);
console.log(Square.isPrototypeOf(square));      // true
console.log(Rectangle.isPrototypeOf(square));   // true
console.log(square.getArea());                  // 100

var triangle = Object.create(Triangle);
triangle.init.call(triangle,3,10);
console.log(Triangle.isPrototypeOf(triangle));  // true
console.log(Rectangle.isPrototypeOf(triangle)); // true
console.log(Square.isPrototypeOf(triangle));    // false
console.log(triangle.getArea());                // 15