[whatwg] Use cases for Node.getElementById (was: Re: Early feedback on header association algorithm)

[João Eiras]

IMO, anyone suggesting a Node.getElementById clearly does not know very  
well how getElementById is supposed to work.
There are ways to transverse a DOM tree currently, either DOM properties  
and methods, XPath, selectors API and such.
Considering ids are required to be unique in the context of a single  
document, implementations can, and do, implement id lookup using optimized  
data structures like a hash table, which is much more performant than  
doing transversal.
So if there is a special node in a document, add an id to it and get its  
reference will be performant (ideally O(1)).

If the uniqueness requirement is removed, then getElementById looses its  
whole meaning and should actually be removed from the specification  
entirely, else then we would need more bloat like getElementById or  
getElementListById and whatever.

If you really need to get the element with id in a subtree, connected or  
disconnected from the main tree, one can use selectors API, DOM  
transversal, XPath, etc.

So, IMO the DOM spec is just fine. What is asked for Node.getElementById  
is already supported by other APIs.