- Parse and examine the AST for a selector
- Calculate the specifity of a selector
- Determine if a single element matches a selector ($().is equivilent) much faster that jQuery
jQuery has an excellent CSS 3 selector engine built in called Sizzle. However, it’s clear focus is on filtering a set of elements down to the set that matches a selector.
jQuery.concrete has a usage pattern quite different from that optimized for by Sizzle. It reuses a small set of selectors (making a more complicated initial parsing step acceptable)
and checks if a single element matches those selectors. In this case, Sizzle can be quite slow.
Usual usage of jQuery selector:
var sel = $.selector(‘#foo’);
element must be a raw DOM object, not a jQuery element, sequence of elements or anything else
jQuery.selector aims to be 100% compatible with Sizzle (except a couple of corner cases, noted below). Sizzle implements most of the CSS 3 spec plus several extensions.
One set of extensions Sizzle has is a set of pseudo-classes that filter the currently selected set. These pseudo-classes are ‘:first’, ‘:last’, ‘:even’, ‘:odd’, ‘:eq’, ‘:nth’, ‘:lt’, ‘:gt’.
These pseudo-classes are not supported in jQuery.selector, as they don’t make sense when the working set is always a single element.
jQuery.selector currently passes the jQuery selector unit test suite, with the exception of the psuedo-classes mentioned above