js判斷瀏覽器版本

<script type="text/javascript">
B = (function(ua){
        var b = {
                msie: /msie/.test(ua) && !/opera/.test(ua),
                opera: /opera/.test(ua),
                safari: /webkit/.test(ua) && !/chrome/.test(ua),
                firefox: /firefox/.test(ua),
                chrome: /chrome/.test(ua)
        };
        var vMark = "";
        for (var i in b) {
                if (b[i]) { vMark = "safari" == i ? "version" : i; break; }
        }
        b.version = vMark && RegExp("(?:" + vMark + ")[\\/: ]([\\d.]+)").test(ua) ? RegExp.$1 : "0";
        
        b.ie = b.msie;
        b.ie6 = b.msie && parseInt(b.version) == 6;
        b.ie7 = b.msie && parseInt(b.version) == 7;
        b.ie8 = b.msie && parseInt(b.version) == 8;
        
        return b;
})(window.navigator.userAgent.toLowerCase());
alert(B.ie8);
</script>