判断浏览器类型

Ext中的判断浏览器类型的代码片段：

   
   var ua = navigator.userAgent.toLowerCase();
    var isStrict = document.compatMode == "CSS1Compat",
        isOpera = ua.indexOf("opera") > -1,
        isSafari = (/webkit|khtml/).test(ua),
        isSafari3 = isSafari && ua.indexOf('webkit/5') != -1,
        isIE = !isOpera && ua.indexOf("msie") > -1,
        isIE7 = !isOpera && ua.indexOf("msie 7") > -1,
        isGecko = !isSafari && ua.indexOf("gecko") > -1,
        isGecko3 = !isSafari && ua.indexOf("rv:1.9") > -1,
        isBorderBox = isIE && !isStrict,
        isWindows = (ua.indexOf("windows") != -1 || ua.indexOf("win32") != -1),
        isMac = (ua.indexOf("macintosh") != -1 || ua.indexOf("mac os x") != -1),
        isAir = (ua.indexOf("adobeair") != -1),
        isLinux = (ua.indexOf("linux") != -1),
        isSecure = window.location.href.toLowerCase().indexOf("https") === 0;