Wow, it's now super clear. Thanks for the detailed explanation.
Just a quick follow up question to quench my curiosity: if I do "list[1]" and
no one has ever asked the list for any element, Gecko will find the first two
matching elements, and store them in the list, if I then immediately do
"list[0]", the first element is returned without walking the DOM (assuming
there are at least two matching elements)?
> querySelector("foo") and getElementsByTagName("foo")[0] can return different
> nodes
Still a bit confused regarding this. If the premise is the selector only
contains characters allowed in a tag name, how can they return different nodes,
maybe I missed something? Unless you mean querySelector(":foo") and
getElementsByTagName(":foo")[0] can return different results, which is obvious.
If by parsing the passed selector (or lookup the cached parsed selectors) you
know it only contains a tag name, why it is a bit harder to optimize? You just
look up the (tagname, root) hash table, no?
> In practice this hasn't come up as a bottleneck in anything we've profiled so
> far
I'm probably prematurely optimizing my code. But nevertheless learned something
quite valuable by asking. Thanks for answering it. :)
