how to select list-items having index value within a certain range?

I want to assign a class to the list-items of an ul li list having 开发者_如何学C.index() value between 10 to 20.

How do I select those elements using jQuery?

<ul>
    <li>One</li>
    <li>Two</li>
    <li>Three</li>
    ...
    ...
    ...
    ...
    li>Thirty</li>
</ul>

So I want something like

$('#id').click(function(){
    //Assign class 'classname' to those li elements 
    //between 10th and 20th (index numbers) in the list
    if([li element's index is between 10 and 20]).addClass('classname');
});

Use slice to get a subset of the elements in a selection:

$('li').slice(10, 20).addClass('classname');

Although I recommend using lonesomeday's method, here is one way to do it purely with selectors:

$("ul li:gt(8) + li:lt(10)").addClass('classname');

Note that as gt and lt use 0 based index, if you want >= 10 you need to use 8 (which is greater than 9).

example: http://jsfiddle.net/GybxF/21/

Altough lonesomeday's answer is correct and probably better. Here is a different solution.

http://jsfiddle.net/E4U6Y/

HTH :)