标签：
无意中看到arr.length === +arr.length;这句代码，然后就去了解了下
这是一种鸭式辨型的判断方法。
鸭式辨型：像鸭子一样走路、游泳和嘎嘎叫的鸟就是鸭子
这句话表示：
a.arr有length这个属性
b.arr.length是一个Number
那么arr可以是array，也可以是string
Jquery中要判断一个变量是否是一个数组的确切方法：Object.prototype.toString.call(arr) === ‘[object Array]‘;
ES6可以通过 Array.isArray(arr)判断数组
那么鸭式辨型一般用在什么地方呢？
一般用在模拟接口的实现。、
js 没有class 和 interface，但是Js的interface可以通过模拟来实现
模拟实现接口有三种方法：
a.注释法（该方法全凭程序自觉去继承实现了）
/* interface People{ function createHead(); function createBody(); } */ var woman = function(name){ //implements People interface this.name = name; } woman.prototype.showName = function(){ alert(this.name); } woman.prototype.createBody = function(){ //实现必要的方法 alert("身体已经创建好"); } woman.prototype.createHead = function(){ alert("头部已经创建好"); }
b.属性检测法/*
interface People{ function createHead(); function createBody(); } */ var woman = function(name){ this.name = name; this.implementsInterfaces = [‘People‘]; } woman.prototype.showName = function(){ alert(this.name); } woman.prototype.createBody = function(){ //实现必要的方法 alert("身体已经创建好"); } woman.prototype.createHead = function(){ alert("头部已经创建好"); } function implement(obj,interfaces){ for(var i=1;i<interfaces.length;i++){ var interfaceName = interfaces[i]; var interfaceFound = false; for(var j=0;j<obj.implementsInterfaces.length;j++){ if(obj.implementsInterfaces[j] = interfaceName){ interfaceFound = true; break; } } if(!interfaceFound){ return false; } } return true; } function isImplememts(instance,interfaces){ //判断对象是否已经继承相应接口 if(!implement(instance,interfaces)){ throw new Error("Object doesn‘t implement a required interface"); }
}
c.鸭式辨型法
//接口类，用来创建接口 var Interface = function(name,motheds){ if(agruments.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;i<motheds.length;i++){ if(typeof motheds[i] !== ‘string‘){ throw new Error(‘Interface constructor expects mothed names to be‘+‘passes in as a string‘); } this.methods.push(motheds[i]); } } Interface.prototype.ensureImplements = function(objs){ if(agruments.length != 1){ throw new Error("Interface constructor called with "+arguments.length+"arguments,but expected exactly 1") } for(var i=0;i<objs.length;i++){ var obj = objs[i]; for(var j=0;j<this.motheds.length;j++){ var mothed = this.methods[j]; if(!obj[mothed] || !typeof obj[mothed] !== ‘function‘){ throw new Error(‘Function Interface.ensureImplements:implements interface‘+this.name+‘,obj.mothed‘+mothed+‘was not found‘); } } } } //创建接口 var People = new Interface(‘People‘,[‘createHead‘,‘createBody‘]); //子类 var Woman = function(name){ this.name = name; this.implementsInterfaces = [‘People‘]; } Woman.prototype.showName = function(){ alert(this.name); } Woman.prototype.createBody = function(){ //实现必要的方法 alert("女人身体已经创建好"); } Woman.prototype.createHead = function(){ alert("女人头部已经创建好"); } //子类 var Man = function(name){ this.name = name; this.implementsInterfaces = [‘People‘]; } Man.prototype.showName = function(){ alert(this.name); } Man.prototype.createBody = function(){ //实现必要的方法 alert("男人身体已经创建好"); } Man.prototype.createHead = function(){ alert("男人头部已经创建好"); } //判断是否实现 Poeple.ensureImplements([‘Woman‘,‘Man‘]);
标签：
原文地址：http://www.cnblogs.com/thonrt/p/5977745.html
