js获取IE版本，while代码很特别

<!DOCTYPE html>

<html>

<head>

    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

    <meta name="viewport" content="initial-scale=1.0, user-scalable=no" />

    <title>百度地图的Hello, World</title>

    <style type="text/css">

        body, html, #allmap { width: 100%; height: 100%; overflow: hidden; margin: 0; }

    </style>

</head>

<body>

<script>

  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;

}());

document.write(ie);

</script>

</body>

</html>