小小子

// Constructor
/*
 * @param name String 接口的名字
 * @param methods Array 接口里面定义的方法
*/
var Interface = function(name, methods){
    //如果购造函数的参数不等于2个，那么抛出异常
    if (arguments.length != 2) {
        throw new Error("Interface constructor called with " + arguments.length +
        "arguments,but expected exactyl 2.")
    }

    this.name = name;
    this.methods = [];
    //方法数组，保证传进来的methods数组中，每一个元素都是字符串类型
    for (var i = 0, len = methods.length; i < len; i++) {
        if (typeof methods[i] !== "string") {
            throw new Error("Interface constructor expects methods names to bo " +
            "passed in asastring.");
        }
        this.methods.push(methods[i]);
    }
}

//Static class methods
Interface.ensureImplements = function(object){
        //如果参数少于2个，抛出异常，object是待判断实现接口的对象
        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++) {
                //inter_face为接口，一定要实现Interface类
                //书中使用interface，因是JavaScript中保留字，所以暂替换为inter_face
                var inter_face = arguments[i];
                if (inter_face.constructor !== Interface) {
                        throw new Error("Function Interface.ensureImplementsexpects arguments " +
                        "two and above to be instances of Interface.");
                }
                for (var j = 0, methodsLen = inter_face.methods.length; j < methodsLen; j++) {
                        //对象中是否含有接口中定义的方法
                        var method = inter_face.methods[j];
                        if (!object[method] || typeof object[method] !== 'function') {
                                throw new Error("Function Interface.ensureImplements: object " +
                                "does not implements the " +
                                inter_face.name +
                                "interface.Method " +
                                method +
                                "was not found.");
                        }
                }
        }
}

//定义接口Composite，实现add,remove,getChild三种方法
var Composite = new Interface('Composite',['add','remove','getChild']);

//定义接口FormItem,实现save方法
var FormItem = new Interface('FormItem',['save']);

//判断对象是否实现了上述两个接口
var object = new Class();
Interface.ensureImplements(object,Composite,FormItem);