user agent check of IE

isIE.js

var isIE = (function() {
  var ua = navigator.userAgent.toLowerCase();
  if (ua.indexOf('msie') >= 0 || ua.indexOf('trident') >= 0) {
    var array = /(msie|rv:?)\s?([\d\.]+)/.exec(ua);
    return (array) ? array[2] : true;
  } else {
    return false;
  }
}());