获得当前IE浏览器的版本

网上抄来的，不晓得出处，转贴如下！

// ---------------------- 
// 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;    }());

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