为什么在document.getElementById-ed之后，为什么对象必须被空为IE？ [英] Why object has to be nulled for IE after it was document.getElementById-ed?

问题描述

我经常在第三方JavaScript代码中看到：

I often see in third party JavaScript code that after:

var el = document.getElementById(elementId);

对象通常被置零，并且沿着这个操作发表评论说它是为IE完成的：

object is often nulled and comment along this operation says that it is done for IE:

el = null; // IE

什么是真正的目的？任何资源？

What's the real purpose? Any resource on that?

推荐答案

通过定义引用，它们会破坏DOM对象和JavaScript对象之间的相应的循环依赖关系，由较旧的IE中的不同子系统控制（因此无法进行垃圾收集）。

By nixing a reference they break the corresponding cyclic dependency between the DOM object and JavaScript objects, which are controlled by different sub-systems in older IE (thus being impossible to be garbage-collected).

例如：

var el = document.getElementById(elementId);
el.onclick = function () { // here the cyclic reference is created
    /...
};

JavaScript子系统现在已经引用了 el 元素，并且DOM子系统（ el 元素）引用了JavaScript对象（函数加上它关闭的内容）。

The JavaScript subsystem has now a reference to the el element, and the DOM subsystem (the el element) has a reference to the JavaScript object (the function plus what it closes in).

不用担心，如果您通过 addEventListener 添加监听器。

You don't have to worry, though, if you add the listeners via addEventListener.

要了解有关常见内存泄漏漏洞的更多信息，请参见 http：// www.ibm.com/developerworks/cn/web/library/wa-memleak/ 。

To read more about common memory leak pitfalls, see http://www.ibm.com/developerworks/web/library/wa-memleak/.

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