Javascript Factory example which returns different (Sub)Classes

subclass-factory-example.js

// class pattern helpers
// 
// @see https://stackoverflow.com/questions/1595611/how-to-properly-create-a-custom-object-in-javascript
// 
Function.prototype.makeSubclass= function() {
	function Class() {
		if ('_init' in this)
			this._init.apply(this, arguments);
	}
	Function.prototype.makeSubclass.nonconstructor.prototype= this.prototype;
	Class.prototype= new Function.prototype.makeSubclass.nonconstructor();
	return Class;
};

Function.prototype.makeSubclass.nonconstructor= function() {};



// Foo base class
var Foo = Object.makeSubclass();

// der constructor wird normalisiert und _init dient als neue constructor function

Foo.prototype._init = function (x, y, text) {
	// default class options
	this._foobar = 'barfoo';

	// parameter zur klasse hinzufügen
	this._x = x;
	this._y = y;
	this._text = text;
};

Foo.prototype.getX = function () {
	return this._x;
};

Foo.prototype.getY = function () {
	return this._y;
};

Foo.prototype.getText = function () {
	return this._text;
};

// Foo construction end

// Bar subclass

var Bar = Foo.makeSubclass();

Bar.prototype.getX = function () {
	return this._x + 50;
};

/*
Constructor extension (ein extra parameter r)

Bar.prototype._init= function(x, y, text, r) {
	Foo.prototype._init.call(this, x, y, text); // gleichzusetzen mit dem super call in java
	
	// add extra parameter
	this._r = r;
};
*/

// Bar subclass end

var Factory = {
	// unterstrich am anfang, zeigt developern an, dass dies eine private property ist
	_classes: {
		default: Foo,
		right: Bar
	},

	// create function
	create: function (x, y, text) {
		var className = 'default';

		if (x > 150) {
			className = 'right';
		}

		return new this._classes[className](x, y, text);
	}
};

var myClass = Factory.create(100, 100, 'foobar'); // Factory gibt ein neues Foo zurück
var secondClass = Factory.create(200, 200, 'foobar'); // Factory gibt ein neues Bar zurück

console.log('myClass.getX() -->', myClass.getX());
console.log('secondClass.getX() -->', secondClass.getX());