jQuery - get the index of a element with a certain class

I have a list like this one:

<li> .... </li>
<li> .... </li>
<li> .... </li>
<li class="active"> .... </li>
<li> .... </li开发者_如何学C>

I want to find out the index (number in the list) of the item with the "active" class element. in this case the index would be 4 (or 3 if we're starting from 0) How can I do that?

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With the .index() :

$('li.active').index()

Working example here:

http://jsfiddle.net/EcZZL/

Edit - added link to the api for .index() per Nick's advice

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Like this:

var index = $("ul li.active").index();

.index() without parameters gives the index of the element with respect to it's siblings, which is what you want in this case.