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I'm still learning about jQuery, but I have not been able to find a solid answer. I know every time you use the jQuery selector $(...) there is a performance cost, but does $(this) have a significant cost where you should cache it before using it a lot?

var $this = $(this);
JCotton
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Jason More
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2 Answers2

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If you're using it a lot, yes it makes sense, or chain, e.g.:

$(this).fadeIn().fadeOut().somethingElse();

If it expensive? No not really in the grand scheme of things...but if you're in a loop the cost multiplies so it's best to cache it. If you're using it more than once it makes sense, how much sense depends on how much performance matters for that bit of code I suppose.

Nick Craver
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Good question, Jason. I imagine the jQuery selector function notices the this keyword fairly efficiently. That said, it does make sense to not make repeated calls to the same selector if you can avoid it. This is where method chaining comes in useful:

$(this).hide().show().hide();

If you're going to use the same selector a lot at different points in the same function, I'd probably make a variable to store the return value of the jQuery selector function. Absent that, I wouldn't worry about it, because it's really a very, very small amount of processing that is done...especially since I'm fairly sure the jQuery library checks for the this keyword (and a string type) before it runs any regular expressions.

treeface
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    jQuery would never see `this`. It would only receive the reference that `this` referred to at that point in the code. It can't treat it specially. – bambams Oct 04 '10 at 16:55
  • Ah ha...and that does make sense. Still, a specific reference to an element surely wouldn't take very much processing before the function returned a value, when compared to passing in a string selector. – treeface Oct 04 '10 at 17:15
  • One of the first checks jQuery is going to do is see if the selector is a DOMElement, and if so simply return the wrapped element. I don't mind people using `$this` because it's good to get in the habit of caching selectors, but in the case of `this` it is pretty irrelevant which one you go with. – Paolo Bergantino Aug 07 '12 at 16:50