Add Different Style to list tag using jquery/javascript

Question

Is there any ways to add different style class to all li in a ul tag using jquery/javascript/php. Consider I have a list as follows

<ul><li>a</li><li>b</li><li>c</li><li>d</li><li>e</li></ul>

I would like to add as follows

<ul><li class='cat1'>a</li><li class='cat2'>b</li><li class='cat3'>c</li><li class='cat4'>d</li><li class='cat5'>e</li></ul>

Answer 1

As simple as:

$('ul').children('li').addClass(function (i) {
    return 'cat' + (i+1);
});

http://api.jquery.com/addClass/