$（'。foo'）。eq（0）比$（'。foo'）快吗？

Question

Suppose I have a huge list of elements with a structure like:

<div class="item">
    <div class="header"></div>
    <div class="body"></div>
    <div class="meta"></div>
    <div class="..."></div>
    ...
</div><!-- .item -->

I've already found an element and now I have to find, let's say, a '.body'. What code will work faster:

$(el).find('.body')

or

$(el).find('.body').eq(0)

In other words, will jQuery stop on the first found element or will it loop through all the elements first and only then it will return an element with a chosen index?

Answer 1

This question is ridiculous. "Is it faster if I add another function or if I leave it out of the equation?" is basically what you're asking:

$(el).find('.body') is about 6-7 times faster: http://jsperf.com/to-eq-or-not-to-eq

Answer 2

Your second example will always be slower, because it only calls an additional method on a jQuery object that contains all the elements matching .body .

The fastest way to get the first matching element is probably the :first selector:

$(el).find(".body:first")

You could also spare one method call by using the context argument to $() , but benchmarks reveal that's actually slower :

$(".body:first", el)  // Slower, don't do that.

Answer 3

.eq(0) is a method call on the object returned by $(el).find('.body') . It can't be faster then $(el).find('.body') alone.

Answer 4

They will nearly same as as .eq('0') is called on the result of find('.body') . The second one is never faster.

Answer 5

$(el).find('.body:first')或$(el).find('.body.eq(0)')在逻辑上会更快，因为（至少）它执行的函数调用较少