Javascript: Detect IE

gistfile1.js

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;
    
}());