document.getElementById是否返回实时dom元素? [英] Does document.getElementById return a live dom element?

问题描述

JavaScript中的 document.getElementById 是否返回实时DOM元素?我有兴趣了解性能原因

Does document.getElementById in JavaScript return a live DOM element? I am interested to know for performance reason

推荐答案

标准和实时"之间的区别通常用于元素的列表. document.getElementById 返回对DOM节点的单个对象引用.一旦节点被获取，引用将始终指向同一节点.

The distinction between standard and "live" is usually used for lists of elements. document.getElementById returns a single object reference to a DOM node. Once the node is acquired the reference will always point to the same node.

<div id="foo"></div>

以 _JS为例:

var foo,
    bar;
foo = document.getElementById('foo'); //gets the div
bar = document.getElementById('bar'); //null
foo.setAttribute('id', 'bar');
console.log(foo.id); //'bar'
console.log(bar.id); //TypeError

由于元素的ID可能已更改，因此引用不会得到更新.

The references don't get updated just because the ID of the element might have changed.

这与诸如 document.getElementsByTagName 之类的东西形成对比，后者返回具有给定标记的元素列表.当元素添加到DOM中或从DOM中删除时，该列表将自动更新.

This is in contrast to something like document.getElementsByTagName which returns a list of elements with the given tag. The list will automatically update when elements are added to or removed from the DOM.

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