jQuery note in Section 5.2.2 of W3C DOM4 Specification

Question

Is there anyone that can explain the note on section 5.2.2 of the W3C DOM4 specification?

Relevant Quote:

Note: The getElementById() method is not on elements for compatibility with older versions of jQuery. If a time comes where that version of jQuery has disappeared, we might be able to support it.

I'm curious how this interface would explicitly cause a problem with jQuery and what versions, does anyone have an example?

Answer 1

To expand on @Nan answer, it probably has something to do with jQuery using getElementById to validate a step in an iteration. Adding this method to HTMLElement would make some conditions validate when part of jQuery code depends on it not validating.

Hard to say exactly which version causes the problem and in exactly which situations, but a quick look to old jQuery versions, you can see that find() in older version isn't compatible with Elements having getElementById method.

Going back to version 1.3, you can try to add the method to HTMLElement and you'll see that it messes the result. More recent version handle this correctly. See snippet:

alert('Without getElementById method on HTMLElement, length of $("div").find("#test") is ' + $('div').find('#test').length);
window.HTMLElement.prototype.getElementById = function(str){
    console.log(str);
    return str;
}

alert('With getElementById method on HTMLElement, length of $("div").find("#test") is ' + $('div').find('#test').length);

<script src="https://code.jquery.com/jquery-1.3.js"></script>
<div id="container"><div id="test"></div></div>