Find IE version using javascript

Many Web designers use browser detection techniques to ensure that their sites display properly when viewed with specific browsers. Some browser detection techniques encounter problems when viewed with later versions of the browser they're tailored for. For example, many Web designers used Cascading Style Sheets (CSS) rules that relied on the implementation of CSS in Microsoft Internet Explorer 6 to detect that version of the browser. When Windows Internet Explorer 7 provided additional support for the Cascading Style Sheets, Level 2 (CSS2) standard, many of these rules (also known as "CSS hacks") failed to detect the new version of the browser. As a result, sites that relied on these rules no longer displayed as intended. When using browser detection techniques, use techniques that support current and future versions of the browser you're targeting.

The most common way to detect Internet Explorer is to use client-side scripting to parse the user-agent string and extract the version number from the version token. The following example shows the preferred way to do this with JavaScript. 

function getInternetExplorerVersion()
// Returns the version of Internet Explorer or a -1
// (indicating the use of another browser).
  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;
function checkVersion()
  var msg = "You're not using Internet Explorer.";
  var ver = getInternetExplorerVersion();

  if ( ver > -1 )
    if ( ver >= 8.0 ) 
      msg = "You're using a recent copy of Internet Explorer."
      msg = "You should upgrade your copy of Internet Explorer.";
  alert( msg );