Question

I’d like to alternate the background color in a HTML un-ordered list without using JQuery.

Answer 1

Best option would be CSS3 :nth-child selector:

#myul li:nth-child(odd) {
    background-color: red;
}
#myul li:nth-child(even) {
    background-color: green;
}

or if for some reason you really need javascript solution:

<style>
    li.even { background-color: red; }
    li.odd { background-color: blue; }
</style>

var ul = document.getElementById('myul');
var items = ul.getElementsByTagName('li');
for (var i = 0; i < items.length; i++) {
    var class = i % 2 == 0 ? 'even' : 'odd';
    items[i].className = class;
}

or as already mentioned you could just generate the classes server-side.