What is the implementation of GetElementByID()?

Question

Can somebody please explain to me the internal implementation of HTML getElementById() method ? Is it traversing whole DOM tree to find the specified element or is it intelligen

Answer 1

It depends on the browser, but most probably use a hash map from id->element. It's true that there are many invalid pages that have duplicate ids. However, the browser will still only return one element, not a collection.

I don't know what you mean by "near by elements" since the method only exists on document.

If you're interested, you can find the implementation for free software browsers such as Firefox and Chrome.