当前位置:Gxlcms > JavaScript > 实例讲解JavaScript中的this指向错误解决方法

实例讲解JavaScript中的this指向错误解决方法

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);
  }
} 

人气教程排行