Does document.getElementById return a live dom element?

Question

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

Answer 1

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.

_{HTML for the example:}

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

_{JS for the example:}

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

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

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.