function getInternetExplorerVersion() {

  var rv = -1; // Return value assumes failure.
  if (navigator.appName == 'Microsoft Internet Explorer') {
    var ua = navigator.userAgent;
    var re  = new RegExp("MSIE ([0-9]{1,}[\.0-9]{0,})");
    if (re.exec(ua) != null)
      rv = parseFloat( RegExp.$1 );
  }
  return rv;
}