JS Bin// source http://jsbin.com/howaza GET IE version.

jsbin.howaza.js

var testCases = [
  ["Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36", -1],
  ["Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:31.0) Gecko/20100101 Firefox/31.0", -1],
  ["Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_0) AppleWebKit/600.1.17 (KHTML, like Gecko) Version/8.0 Safari/600.1.17", -1],
  ["Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.57 Safari/537.36", -1],
  ["Mozilla/5.0 (Windows NT 6.2; WOW64; rv:23.0) Gecko/20100101 Firefox/23.0", -1],
  ["Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 2.0.50727)", 7],
  ["Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Win64; x64; Trident/6.0)", 10],
  ["Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)", 9],
  ["Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)", 8],
  ["Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11.0) like Gecko", 11]
];

function testIe(){
  var numOfCases = testCases.length;
  for (var i =0; i < numOfCases; i++) {
    var agent = testCases[i][0],
        version = testCases[i][1];
    console.log(getIEversion(agent) === version);
  }
}

function getIEversion(str){
  var sl = str.toLowerCase();
  if (sl.indexOf('msie')!== -1) {
    return parseInt(sl.split('msie')[1], 10);
  } 
  if(sl.indexOf('trident')!== -1) {
    return parseInt(sl.split(' rv:')[1], 10);
  }
  
  return -1;
}