decorator patters exploring

abstract_decorators.js

// Instructions: Copy past this into chrome console. - BEGIN

// 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;
    }
};
//
// Instructions: Copy past this into chrome console. - END
//
// Demo remaining lines individually


// Instantiation of the macbook
var myMacbookPro = new MacbookPro();

// IN CONSOLE, Outputs: 900.00
myMacbookPro.getPrice()

// Decorate the macbook
var decoratedMacbookPro = new CaseDecorator( myMacbookPro );

// IN CONSOLE, This will return 945.00
decoratedMacbookPro.getPrice()