Javascript IE检测，为什么不使用简单的条件注释？[重复]

James Padolsey在GitHub上放了一些代码片段，我将在这里引用：

// ----------------------------------------------------------// 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 @jdaltonvar 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;}());

当然，所有的荣誉都应该归詹姆斯所有，我只是信使（但如果我的复制粘贴操作有误，请射击信使）。

还要看看创建的叉子。保罗·爱尔兰（PaulIrish）在评论中解释了内部工作原理。