需要对这个简单的代码（js）ty的解释！(Explanation on this javascript check)

需要对这个简单的代码（js）ty的解释！(Explanation on this javascript check) function doSomething(e) { var targ; if (!e) var e = window.event; //<<<< what does it do this check? if (e.target) targ = e.target; }

这很简单，我不能得到它:)为什么我们需要检查这个？ 一个解释将是非常好的，谢谢...

function doSomething(e) { var targ; if (!e) var e = window.event; //<<<< what does it do this check? if (e.target) targ = e.target; }

Why do we need to check this?

最满意答案

这增加了与旧的（Internet Explorer？）浏览器的兼容性，这些浏览器不支持将event对象传递给处理程序，而是将其定义在窗口对象上。

var e = window.event也不需要var e = window.event因为它已经被声明（参数）。

它也可以写成e = e || window.event; e = e || window.event;

This adds compatibility with older (Internet Explorer?) browsers that didn't support passing the event object to handlers but instead defined them on the window object.

Also the var is not needed in var e = window.event because it's already declared (parameter).

It can also be written as e = e || window.event;