JavaScript to detect IE version using conditional tags and add classes to the html tag.

detect_ie.js

window.ie = (function() {
  var undef,
    v = 3,
    htmlClass = document.documentElement.className,
    div = document.createElement('div'),
    all = div.getElementsByTagName('span');

  do {
    div.innerHTML = '<!--[if gt IE ' +  (++v) + ']><span></span><!endif]-->';
  } while (all[0]);
  
  return v > 4 ? v : undef;
})();

(function() {
  var ieClass = '';
  // add classes to html
  switch (window.ie) {
    case 9:
      ieClass = 'ie9';
      break;
    case 8:
      ieClass = 'lt-ie9 ie8';
      break;
    case 7:
      ieClass = 'lt-ie9 lt-ie8 ie7';
      break;
  }
  document.documentElement.className = ieClass;

})();