Question

78

$.each() vs for() loop - and performance

rated 0 times [ 83] [ 5] / answers: 1 / hits: 75919 / 12 Years ago, thu, august 9, 2012, 12:00:00

These are mainly just some things I've been wondering, maybe someone can give me a little more insight on them, i'll share what i've noticed so far as well!

First thing i've been wondering... is there any difference good or reason to use:

$('element').each(function (i, el) { });

-- versus --

$.each($('element'), function (i, el) { });

Looking at the jQuery docs I can't see any rhyme or reason for one or the other (maybe you know an instance or additional things one can do over the other.

But more importantly I'm concerned with speed here

// As opposed to $.each() looping through a jQuery object

// -- 8x faster 

for (var i = 0, $('.whatever').length; i < len; i++) {

    $('.whatever')[i] // do stuff

}

If you check out this jsFiddle DEMO here, you'll see the difference in speed is basically equivalent with either of them, but more importantly I feel like I should always be using for() loops...

I was just unit testing (looping through each of 5 different scenario functions, 50,000 times), simply looping through a bunch of list items, and setting a data-newAttr, nothing special.

QUESTION :: I guess my biggest question is, why not always use for loops while iterating through an object?? Is there even a point to using $.each()? Do you always use for() loops even when going through jQuery objects?

jsFiddle DEMO here

Function type:                  Execution Time:

_testArea.each() + $(this)               1947   <-- using $(this) slows it down tremendously

$.each()         + $(this)               1940

_testArea.each() + el(plain JS)           458   <-- using the Element speeds things up

$.each()         + el(plain JS)           452

for() loop       + plainJS[0] iteration   236   <-- over 8x faster

Just my 2cents. :)

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chelseyn

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4 Years ago

answered 12 Years ago breap · Accepted Answer

One thing that .each() allows you to do that can't be done with a for loop is chaining.

$('.rows').each(function(i, el) {

    // do something with ALL the rows

}).filter('.even').each(function(i, el) {

    // do something with the even rows

});

I played around with your JSFiddle to see how chaining would influence performance in cases where you have to loop through subsets of the original set of matched elements.

The result wasn't all that unexpected, although I think the overhead of end() was exaggerated here because of the combination of few elements and many loops. Other than that: plain JS loops are still slightly faster, but whether that weighs up to the added readability of .each() (and chaining) is debatable.