Question

Is this faster:

$(document.links).filter('a.someClass')

than just plain old this:

$('a.someClass')

?

I don’t see anywhere in jQuery’s code the utilization of document.links
which gives you the collection of links on the document right away,
than, it would seem, it would be faster to just filter in the collection
instead of all the DOM nodes, which is alot more nodes to go over.

Answer 1

Theoretically, iterating document.links will be a bit faster than jQuery’s Sizzle selector library. However:

• not the way you’re doing it with filter, which gives jQuery just as much work to do than it would have to do using Sizzle to pick the elements in the first place;

• document.links won’t necessarily give you exactly the same as $('a'), as a-without-href doesn’t appear in the links collection.

• the direct $('a.someClass') method will be much faster than even manually iterating document.links in modern browsers, because that method will just transfer control to the browser’s own implementation of document.querySelectorAll('a.someClass'), which will be much faster than anything your or Sizzle could do sniffing at DOM Nodes yourself.

(There is one slightly faster method than querySelectorAll, which jQuery doesn’t use yet: document.getElementsByClassName('someClass'). Again, it’s only in modern browsers though, and IE8 doesn’t have it where it does have querySelectorAll. In practice it’s probably not worth bothering about too much as querySelectorAll is already very fast.)