JavaScript IE Version Detection, IE6-10 and IE Mobile

gistfile1.js

// ----------------------------------------------------------
// A short snippet for detecting versions of IE:
// Uses a combination of object detection and user-agent 
// sniffing.
// ----------------------------------------------------------
// If you're not in IE then:
//     ie === NaN  // falsy
// If you're in IE then you can determine which version:
//     ie === 7; // IE7
// Thus, to detect IE:
//     if (ie) {}
// And to detect the version:
//     ie === 6 // IE6
//     ie > 7 // IE8, IE9 ...
//     ie < 9 // Anything less than IE9
// ----------------------------------------------------------


var ie = ( !!window.ActiveXObject && +( /msie\s(\d+)/i.exec( navigator.userAgent )[1] ) ) || NaN;

Sometimes I see "Unable to get property '1' of undefined or null reference" because
/IEMobile/(\d+.?(\d+)?)/.exec( navigator.userAgent ) is null
if "IEMobile" string is not exists in the navigator.userAgent.
I have used a code below for resolving of problem:

var ieMobile = /IEMobile/(\d+.?(\d+)?)/.exec( navigator.userAgent );
ieMobile = ( !! window.ActiveXObject && ieMobile && (ieMobile.length >= 2) && +( ieMobile[1] ) ) || NaN;