javascript - How is getElementById() implemented in machine code and why is not part of a DOM element when it is a part of a DOM document?

Question

Why isn't getElementById() part of a DOM element when at the same time it is a part of a DOM document, keeping in mind that document stands higher in a hierarchy than an element. How exactly is getElementById() implemented in machine code of browsers?

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question from:https://stackoverflow.com/questions/65870425/how-is-getelementbyid-implemented-in-machine-code-and-why-is-not-part-of-a-dom

Answer 1

id values must be unique in the document, so there's very little need to look for an element by id within another element. Just look for it on the document.

In the rare case you need to look for an element by id only within another element's descendants, you can use querySelector with an ID selector:

const e = someElement.querySelector("#the-id");

...but again, it's a rare use case that likely suggests that ids are being misused.