jQuery selector efficiency

Question

I have a quick Bing and can't really find the answer.

If I have a whack of code that uses $('something here') 150 times, would it be more efficient to:

var item = $('something here')

Pretty silly questions I know, but would it be more efficent as jQuery only has to find the item once?

Answer 1

Yes, storing the resulting jQuery object is tremendously more efficient and may be magnitudes faster. Each time you use a selector you are initiating a new search. jQuery does not cache results. If you store the resulting jQuery object in a variable, you are effectively eliminating the need to run the search over and over again each time.

Answer 2

According to this article, it is more efficient to assign the selector to a variable, which makes sense since jQuery does not need to scan the DOM for elements matching the selector again.

http://geekswithblogs.net/renso/archive/2009/07/14/jquery-selector-efficiencycost-impact.aspx

It also provides other tips. For instance, try to avoid using the class selector alone. Interestingly, a selector such as $('#someID') is faster than $('div#someID').

Answer 3

Please go through this article to know exactly how jQuery is working behind the screen. Very well explained.

http://net.tutsplus.com/tutorials/javascript-ajax/quick-tip-jquery-newbs-stop-jumping-in-the-pool/