IE Detection in JavaScript

detectIE.js

// just a slimmed-down implementation of browser testing for IE in JavaScript
// based on code I found online
/**
 * detect IE
 * returns version of IE or false, if browser is not Internet Explorer
 */
function detectIE() {
  var ua = window.navigator.userAgent;
  var msie = ua.indexOf('MSIE ');
  if (msie > 0) {
    // IE 10 or older => return version number
    return parseInt(ua.substring(msie + 5, ua.indexOf('.', msie)), 10);
  }
  var trident = ua.indexOf('Trident/');
  if (trident > 0) {
    // IE 11 => return version number
    var rv = ua.indexOf('rv:');
    return parseInt(ua.substring(rv + 3, ua.indexOf('.', rv)), 10);
  }
  var edge = ua.indexOf('Edge/');
  if (edge > 0) {
    // Edge (IE 12+) => return version number
    return parseInt(ua.substring(edge + 5, ua.indexOf('.', edge)), 10);
  }
  // other browser
  return false;
}

// Get IE or Edge browser version
var ieVersion = detectIE();

if (ieVersion === false) {
  console.log('NOT ie/edge');
} else if (ieVersion >= 12) {
  console.log('edge ' + ieVersion);
} else {
  console.log('ie ' + ieVersion);
  ieTest();
}