看以下对象定义：

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

如许能一般挪用

jane.display();

下面的挪用会失足：

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

由于，this指向已转变，准确的体式格局以下：

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

一切函数都有其特别的this变量，以下面的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);
        });
    }
}   

挪用sayHiToFriends会发生一个毛病：

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

解决方案一：将this保存在差别的变量中

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：应用forEach的第二个参数，它能够给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);
    }
}