/**
* Return true to include current element
* Return false to exclude current element
*/
$.expr[':']['nth-of-type'] = function(elem, i, match) {
if (match[3].indexOf("n") === -1) return i + 1 == match[3];
var parts = match[3].split("+");
return (i + 1 - (parts[1] || 0)) % parseInt(parts[0], 10) === 0;
};
Test case – (check in IE or rename the selector)
You can of course add even & odd too:
match[3] = match[3] == "even" ? "2n" : match[3] == "odd" ? "2n+1" : match[3];