​

// Utilities required for this example

// ========================================

​

// extend()

// Extend an object a with the properties

// in object b

function extend( a, b ){

    for( var key in b )

        if( b.hasOwnProperty(key) )

            a[key] = b[key];

    return a;

}

// Interface()

// An interface constructor

// Note: interface is a reserved word in JavaScript and is only used here for demonstration purposes.

var Interface = function (name, methods) {

        if (arguments.length != 2) {

            throw new Error("Interface constructor called with " + arguments.length + "arguments, but expected exactly 2.");

        }

        this.name = name;

        this.methods = [];

        for (var i = 0, len = methods.length; i < len; i++) {

            if (typeof methods[i] !== 'string') {

                throw new Error("Interface constructor expects method names to be " + "passed in as a string.");

            }

            this.methods.push(methods[i]);

        }

    };

// Static class method.

Interface.ensureImplements = function (object) {

    if (arguments.length < 2) {

        throw new Error("Function Interface.ensureImplements called with " + arguments.length + "arguments, but expected at least 2.");

    }

    for (var i = 1, len = arguments.length; i < len; i++) {

        var interface = arguments[i];

        if (interface.constructor !== Interface) {

            throw new Error("Function Interface.ensureImplements expects arguments" + "two and above to be instances of Interface.");

        }

        for (var j = 0, methodsLen = interface.methods.length; j < methodsLen; j++) {

            var method = interface.methods[j];

            if (!object[method] || typeof object[method] !== 'function') {

                throw new Error("Function Interface.ensureImplements: object " + "does not implement the " + interface.name + " interface. Method " + method + " was not found.");

            }

        }

    }

};

​

​

// Macbook decorator abstract decorator class

​

var MacbookDecorator = function( macbook ){

​

    Interface.ensureImplements( macbook, Macbook );

    this.macbook = macbook;

​

};

​

MacbookDecorator.prototype = {

    addEngraving: function(){

        return this.macbook.addEngraving();

    },

    addParallels: function(){

        return this.macbook.addParallels();

    },

    add4GBRam: function(){

        return this.macbook.add4GBRam();

    },

    add8GBRam:function(){

        return this.macbook.add8GBRam();

    },

    addCase: function(){

        return this.macbook.addCase();

    },

    getPrice: function(){

        return this.macbook.getPrice();

    }

};

​

/////

​

var CaseDecorator = function( macbook ){

   this.macbook = macbook;

};

​

// Let's now extend (decorate) the CaseDecorator with

// a MacbookDecorator

extend( CaseDecorator, MacbookDecorator );

​

CaseDecorator.prototype.addCase = function(){

    return this.macbook.addCase() + "Adding case to macbook";

};

​

CaseDecorator.prototype.getPrice = function(){

    return this.macbook.getPrice() + 45.00;

};

​

var Macbook = new Interface( "Macbook",

  ["addEngraving",

  "addParallels",

  "add4GBRam",

  "add8GBRam",

  "addCase"]);

​

// A Macbook Pro might thus be represented as follows:

var MacbookPro = function(){

    // implements Macbook

};

​

MacbookPro.prototype = {

    addEngraving: function(){

    },

    addParallels: function(){

    },

    add4GBRam: function(){

    },

    add8GBRam:function(){

    },

    addCase: function(){

    },

    getPrice: function(){

      // Base price

      return 900.00;

    }

};

////

​

​

// Instantiation of the macbook

var myMacbookPro = new MacbookPro();

​

// Outputs: 900.00

console.log( myMacbookPro.getPrice() );

​

// Decorate the macbook

var decoratedMacbookPro = new CaseDecorator( myMacbookPro );

​

// This will return 945.00

console.log( decoratedMacbookPro.getPrice() );