Question

Is selecting by ID-only (or a single identifier) faster than when adding additional identifiers?

For example

$('#element')

vs

$('#container #element')

or even more specific:

$('body div#container div#element')

?

Answer 1

$('#element') should be fastest, followed by $('div'). These map to the native functions document.getElementById and document.getElementsByTagName. Anything more complex has to go through complex scripting and document searching.

On everything but IE6, 7, and 8, $('.class') also map to the new document.getElementsByClassName function as well, but this is slower than the other two and still has to go through Sizzle if the browser doesn’t support it.