接口设计

// Constructor.接口对象

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.");
            }
        }
    } 
};

/* How to Use */
//定义一些接口
var Composite = new Interface('Composite',['add','remove','getChild']);
var FormItem = new Interface('FormItem',['save']);
//检查Object是否实现接口Composite和FormItem的方法
Interface.ensureImplements(Object, Composite, FormItem);