接口在工厂模式中起着很重要的作用，如果不对对象进行某种类型检查的以确保其实现了必要的方法，工厂模式的好处也就所剩无几了，举个简单的例子。

Interface.js

1 // Constructor. 2  3 var Interface = function(name, methods) { 4     if(arguments.length != 2) { 5         throw new Error("Interface constructor called with " + arguments.length 6           + "arguments, but expected exactly 2."); 7     } 8      9     this.name = name;10     this.methods = [];11     for(var i = 0, len = methods.length; i < len; i++) {12         if(typeof methods[i] !== 'string') {13             throw new Error("Interface constructor expects method names to be " 14               + "passed in as a string.");15         }16         this.methods.push(methods[i]);        17     }    18 };    19 20 // Static class method.21 22 Interface.ensureImplements = function(object) {23     if(arguments.length < 2) {24         throw new Error("Function Interface.ensureImplements called with " + 25           arguments.length  + "arguments, but expected at least 2.");26     }27 28     for(var i = 1, len = arguments.length; i < len; i++) {29         var interface = arguments[i];30         if(interface.constructor !== Interface) {31             throw new Error("Function Interface.ensureImplements expects arguments "   32               + "two and above to be instances of Interface.");33         }34         35         for(var j = 0, methodsLen = interface.methods.length; j < methodsLen; j++) {36             var method = interface.methods[j];37             if(!object[method] || typeof object[method] !== 'function') {38                 throw new Error("Function Interface.ensureImplements: object " 39                   + "does not implement the " + interface.name 40                   + " interface. Method " + method + " was not found.");41             }42         }43     } 44 };

声明一个接口Bicycle，定义该接口应该有哪些方法

1 var Bicycle = new Interface("Bicycle",["assemble","wash","ride","repair"]);

构造一个简单的工厂BicycleShop，根据传递的模型，卖出不同类型的自行车。

1 var BicycleShop  = function(){}; 2      3     BicycleShop.prototype = { 4         sellBicycle:function(model){ 5             var bicycle; 6             switch(model){ 7                 case "The Speedster": 8                     bicycle = new Speedster(); 9                     break;10                 case "The Lowrider":11                     bicycle = new Lowrider();12                     break;13                 case "The Comfort Cruiser":14                 default:15                     bicycle = new ComfortCruiser();16             }17             Interface.ensureImplements(bicycle,Bicycle);18             bicycle.assemble();19             bicycle.wash();20             return bicycle;21         }22     }

建立一个Speedster类型的自行车，且该类提供了必要的方法

1 var Speedster = function(){ 2     }; 3     Speedster.prototype = { 4         assemble:function(){ 5             console.log("assemble method is exected"); 6         }, 7         wash:function(){ 8             console.log("wash method is exected"); 9         },10         ride:function(){11             console.log("ride method is exected");12         },13         repair:function(){14             console.log("repair method is exected");15         }16     }

创建一个工厂，传入模型参数

1 var californiaCruisers = new BicycleShop();2 californiaCruisers.sellBicycle("The Speedster");

结果：

 然而，如果需要加入一款新车型，那么必须为此修改BicycleShop代码，哪怕这个类的实际功能并没有发生变化。因此，更好的解决办法是把SellBicycle中的方法中创建实例的这部分交给一个简单的工厂。

1 var BicycleFactory = { 2         createBicycle:function(model){ 3             var bicycle; 4             switch(model){ 5                 case "The Speedster": 6                     bicycle = new Speedster(); 7                     break; 8                 case "The Lowrider": 9                     bicycle = new Lowrider();10                     break;11                 case "The Comfort Cruiser":12                 default:13                     bicycle = new ComfortCruiser();14             }15             Interface.ensureImplements(bicycle,Bicycle);16             return bicycle;17         }18     }19 20     var BicycleShop  = function(){};21     22     BicycleShop.prototype = {23         sellBicycle:function(model){24             var bicycle = BicycleFactory.createBicycle(model);25             bicycle.assemble();26             bicycle.wash();27             return bicycle;28         }29     }