看如下对象定义：

'use strict'var jane = { name ： ‘Jane', display : function(){ retrun 'Person named ' + this.name; }};

这样能正常调用

jane.display();

下面的调用会出错：

var func = jane.display;func()TypeError: Cannot read property 'name' of undefined

因为，this指向已经改变，正确的方式如下：

var func2 = jane.display.bind(jane);func2()'Penson named Jane'

所有函数都有其特殊的this变量，如下面的forEach

var jane = { name : 'Jane', friends: ['Tarzan', 'Cheeta'], sayHiToFriends: function(){ 'use strict'; this.friends.forEach(function(friend) { // 'this' is undefined here console.log(this.name + ' says hi to '+ friend); }); }}

调用sayHiToFriends会产生一个错误：

jane.sayHiToFriends()TypeError: Cannot read property 'name' of undefined

解决方案一：将this保存在不同的变量中

var jane = { name : 'Jane', friends: ['Tarzan', 'Cheeta'], sayHiToFriends: function(){ 'use strict'; var that = this; this.friends.forEach(function(friend) { console.log(that.name + ' says hi to '+ friend); }); }}

解决方案二：利用forEach的第二个参数，它可以给this指定一个值

var jane = { name : 'Jane', friends: ['Tarzan', 'Cheeta'], sayHiToFriends: function(){ 'use strict'; this.friends.forEach(function(friend) { console.log(this.name + ' says hi to '+ friend); }, this); }}