javascript 实现 接口编程

// 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

接口是基于实例方法的，如果未实现，静态方法就会抛出错误。