// Constructor.

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.");

            }

        }

    }

};

//定义了一个USB接口

var USB = new Interface('USB', ['read', 'write']);

//FlashDisk类，需要实现USB接口

function FlashDisk() {

}

FlashDisk.prototype.read = function () {

};

FlashDisk.prototype.write = function () {

};

//MP3类，同样需要实现USB接口

function MP3() {

}

MP3.prototype.read = function () {

};

MP3.prototype.write = function () {

};

//没有实现USB接口或没有全部实现

function BadDevice() {

}

BadDevice.prototype.write = function () {

};

//没有实现该接口

/*BadDevice.prototype.read = function () {

}*/

//USB设备管理类

function USBManager() {

  this.devices = [];

}

USBManager.prototype.add = function (device) {

  Interface.ensureImplements(device, USB); //确保添加的设备实现了USB接口，没有实现的话会抛出异常

  this.devices.push(device);

};

var disk = new FlashDisk();

var mp3 = new MP3();

var bad = new BadDevice();

var manager = new USBManager();

manager.add(disk);

manager.add(mp3);

manager.add(bad); //此处会抛出异常