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JS能把类模仿得惟妙惟肖，也可以模仿接口，参考pro javascript design pattern一书，主要有3种方式
注释（Comment)
这种不用多说了，就是在注释里写明接口定义了哪些方法，哪些地方需要实现什么接口。好处是不会增加任何多的对象或函数，也不会影响执行效率。坏处也很明显，一切靠自觉，而且没有错误提示。
属性检查（Attribute Checking）
function Dog() { this.implementInterfaces = [‘Animal‘]; } function play(dog) { implement(dog, ‘Animal‘); dog.eat(); dog.run(); } function implement(obj) { var interfaceName, interfaceFound, i, j, len; for (i = 1; i < arguments.length; i += 1) { interfaceName = arguments[i]; interfaceFound = false; for (j = 0, len = obj.implementInterfaces.length; j < len; j += 1) { if (interfaceName == obj.implementInterfaces[j]) { interfaceFound = true; break; } } if (!interfaceFound) { throw new Error(interfaceName + " was not implemented"); } } }
这种方式的好处是有错误提示，但是仍然要靠自觉，即使检查通过了，也不能确保就真的实现了接口的方法。
Duck Typing
function Interface(name, methods) { var i, len; if (arguments.length !== 2) { throw new Error("exactly 2 arguments are expected"); } this.name = name; this.methods = []; for (i = 0, len = methods.length; i < len; i += 1) { if (typeof methods[i] !== ‘string‘) { throw new Error("method name is expected to be passed in as a string"); } this.methods.push(methods[i]); } } Interface.ensureImplements = function (obj) { var i, j, interface, method, l, len = arguments.length; if (len < 2) { throw new Error("at least 2 arguments are expected"); } for (i = 1; i < len; i += 1) { interface = arguments[i]; if (interface.constructor !== Interface) { throw new Error("instances of Interface are expected"); } for (j = 0, l = interface.methods.length; j < l; j += 1) { method = interface.methods[j]; if (typeof obj[method] !== ‘function‘) { throw new Error("Method " + method + "() of Interface " + interface.name + " was not found"); } } } }; var Animal = new Interface(‘Animal‘, [‘eat‘, ‘run‘]),
dog = new Dog(); Interface.ensureImplements(dog, Animal);
"If it walks like a duck and quacks like a duck, it‘s a duck"，这个方法不去管类有没有实现接口，而是把注意力放在实例上，毕竟接口里的方法最后都要落在实例上，只要确保实例含有同名方法，就认为它实现了接口，这也是duck type命名的由来。
接口的实现并不复杂，重要的是恰当的判断是否需要使用接口。
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原文地址：http://www.cnblogs.com/coiorz/p/4811569.html
