javascript - 在javascript中为什么使用 "var that = this "

Question

嗨，我是 JavaScript 的新手

使用这条线有什么好处

var that = this

一个例子

function Person( firstname, lastname, age ) {

this.firstname = firstname;

this.lastname = lastname;

this.age = age;

getfullname = function() {

return firstname + “ “ + lastname; }

var that = this;

this.sayHi = function() {

document.write( “Hi my name is “ + getfullname() + “ and I am “ + that.age + “years old.”);

} }

谢谢

Answer 1

this 是上下文相关的。使用 that 可确保在调用 sayHi 时它可以使用调用 getfullname 时的 this 值。