/**

 * Returns the version of Internet Explorer or a -1

 * (indicating the use of another browser).

 */

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;

}

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."

        else

            msg = "You should upgrade your copy of Internet Explorer.";

    }

    alert( msg );

}

// ----------------------------------------------------------

// A short snippet for detecting versions of IE in JavaScript

// without resorting to user-agent sniffing

// ----------------------------------------------------------

// If you're not in IE (or IE version is less than 5) then:

//     ie === undefined

// If you're in IE (>=5) 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

// ----------------------------------------------------------

// UPDATE: Now using Live NodeList idea from @jdalton

var ie = (function(){

    var undef,

        v = 3,

        div = document.createElement('div'),

        all = div.getElementsByTagName('i');

    while (

        div.innerHTML = '<!--[if gt IE ' + (++v) + ']><i></i><![endif]-->',

        all[0]

    );

    return v > 4 ? v : undef;

}());