Detect IE version 5-9 (based on conditional comments)

gistfile1.js

/* Don't forget, the currently unreleased IE10 is supposedly dropping support for conditional comments
   so we'll need something else in this function to detect IE10 (hopefully, we'll never need to) */

var ie = (function(){ 
	var undef,
		v = 3,
		div = document.createElement('div'),
		all = div.getElementsByTagName('i'); 
	while (
		div.innerHTML = '<!--[if gt IE ' + (++v) + ']><i></i><![endif]-->',
		all[0]
	); 
	return v > 4 ? v : undef; 
}());


if (ie == 8) { /*Do something for IE8*/ }