使用JavaScript或jQuery如何检查窗口上是否存在事件？ [英] Using JavaScript or jQuery how to check if event exists on the window?

问题描述

我已经将一个事件附加到'window'对象，我想通过代码检查它是否存在。

I've attached an event to the 'window' object, and I would like to check that it's there via code.

window.addEventListener('beforeunload', function(e){ /*...*/ }, false)

尝试

我尝试过简单的jQuery，没有运气。我对 jsFiddle 进行了更多尝试。

Attempts

I've tried the simple, and jQuery, without luck. I have more attempts up on jsFiddle.

window.beforeunload //is undefined as is window.onbeforeunload

$(window).data('events') //not working either

这可能吗？

有类似的问题（这里和这里）关于DOM和其他元素，但是我尝试过的方法都没有奏效。

There are similar questions (here and here) about the DOM, and other elements, but none of the approaches in those that I have tried have worked.

推荐答案

你可以使用 operator ...

You can use the in operator...

'onbeforeunload' in window;  // true (if supported)

---

如果支持，该属性将存在，​​但值将为 null 。

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