时间:2021-07-01 10:21:17 帮助过:35人阅读
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); } }