JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://ajax.microsoft.com/ajax/jquery.validate/1.7/jquery.validate.js"></script>
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/ui-lightness/jquery-ui.css">
<ul class='items'>
    <li>one</li>
    <li>two</li>
    <li>three</li>
</ul>

JavaScript

var third = document.getElementsByTagName('li')[2];
alert(get_css_selector(third));

function get_css_selector(elem) {
    var tag = elem.tagName.toLowerCase();
    return tag + ':eq(' + $(tag).index(elem) + ')';
}