简介

javascript是一门面向对象的语言，在javascript中，一切都是对象。对象的属性包括了数据属性和访问器属性，根据实际情况，我们又可以把对象的属性分为原型属性和实例属性。下面我们以三个例子来分别看看 for...in...,Object.keys和Object.getOwnPropertyNames 在遍历对象属性时的不同

for...in...

var testData = ["one","two","three"]var testMap = {"index1":1,"index2":2,"index3":3};function Person(name,sex){  this.name = "Thomas";  this.sex = "male";}Person.prototype.getName = function(){ return this.name} //拓展prototype属性for(var i in testData){  console.log(i);  //输出0,1,2   }for(var i in testMap){  console.log(i);// "index1","index2","index3"  返回所有的}var personOne = new Person();for(var prop in personOne){  console.log(prop) //name,sex,getName 返回可枚举的属性，包括原型链上的}

这里我们看到，利用for...in..遍历test时，输出的是0,1,2。为什么是这样子呢？其实我们可以把数组看成是

｛  0:"one",  1:"two",  2:"three" ｝

这就是我们为什么可以通过test[0],test[1],test[2]来访问到这些数据的重要原因。

Object.keys()

var testData = ["one","two","three"]var testMap = {"index1":1,"index2":2,"index3":3};function Person(name,sex){  this.name = "Thomas";  this.sex = "male";}Person.prototype.getName = function(){ return this.name} //拓展prototype属性console.log(Object.keys(testData)); //["0", "1", "2"]console.log(Object.keys(testMap)); // "index1","index2","index3"  返回所有的var personOne = new Person();console.log(Object.keys(personOne));//["name", "sex"],无法获取原型链上的属性

Object.getOwnPropertyNames()

var testData = ["one","two","three"]var testMap = {"index1":1,"index2":2,"index3":3};function Person(name,sex){  this.name = "Thomas";  this.sex = "male";}Person.prototype.getName = function(){ return this.name} //拓展prototype属性console.log(Object.getOwnPropertyNames(testData)); //["0", "1", "2","length"],包括可枚举和不可枚举的属性console.log(Object.getOwnPropertyNames(testMap)); // "index1","index2","index3"  var personOne = new Person();console.log(Object.getOwnPropertyNames(personOne));//["name", "sex"],无法获取原型链上的属性

可以看到

备注：对象属性的可枚举或者不可枚举可以通过Object.defineProperty来重新定义，例如，在前面的程序中，我们重新修改一下代码：

function Person(name,sex){  this.name = "Thomas";  this.sex = "male";}Person.prototype.getName = function(){ return this.name} //拓展prototype属性var personOne = new Person();Object.defineProperty(personOne,"name",{  enumerable: false,  configurable: false,  writable: false,})console.log(Object.keys(personOne));//结果是：["sex"]，原本是 ["name","sex"].这是name属性变得不可枚举

参考链接：