简单工厂模式(Simple Factory)

gistfile1.js

// javascript

function Shape(){};
Shape.prototype.draw = function(){};

function Circle(){};
Circle.prototype = new Shape();

function Square(){};
Square.prototype = new Shape();

function ArtTracer(){};
ArtTracer.factory = function(type){
    var type_str = ({}).toString.call(type);
    if(type == '[object Function'] && window[type]){
         return new window[type]();    
    }else{
        throw new Error('The type ' + type + ' undefined.');
    }
};

var circle_obj = ArtTracer.factory('Circle');