Short alias for querySelectorAll
var $ = Selector.$,
$$ = Selector.$$;
...
var btns = $$('ul > li .btn', parentNode);
If you should supports old browsers, import sizzle or jquery on your page.
<!--[if lt IE 9]>
<script src="sizzle.js"></script>
<![endif]-->
<script>
var elements = Selector.$$('.works .with .sizzle');
...
</script>