javascript关于检测浏览器和操作系统的问题

1.方法学：

最好是检测浏览器的最小版本，这样才不会当版本升级之后不断添加新的内容进去。

理想的方式：

if(isMinIE5){

//code

}

直接检查准确的版本的缺点：

if(isMinIE5||isIE6){

　　//code

}

但是当版本升级之后加入升级到版本10：

if(isMinIE5||isIE6||isIE7||isIE8||isIE9||isIE10){

//code

}

相对于直接检测浏览器的最小版本更麻烦

2.具体的步奏以及注释：（user-agent方法）

var sUserAgent = navigator.userAgent;                                                             //将user-agent字符串保存到本地变量之中去
var fAppVersion = parseFloat(navigator.appVersion);                                     //获得本地浏览器的版本

function compareVersions(sVersion1, sVersion2) {              //用split()方法将两个版本号转换为数组，用 "."作为字符的分隔符
    var aVersion1 = sVersion1.split(".");
    var aVersion2 = sVersion2.split(".");

//保证两个版本的各个数字的长度也一样，否则在较短的一个版本末尾添加0至两个版本的长度相等
    if (aVersion1.length > aVersion2.length) {           
        for (var i=0; i < aVersion1.length - aVersion2.length; i++) {
            aVersion2.push("0");
        }
    } else if (aVersion1.length < aVersion2.length) {
        for (var i=0; i < aVersion2.length - aVersion1.length; i++) {
            aVersion1.push("0");
        }  
    }
   //比较两个版本的大小，版本1大于版本2返回1，反之，返回-1，相等返回0
    for (var i=0; i < aVersion1.length; i++) {

if (aVersion1[i] < aVersion2[i]) {
            return -1;
        } else if (aVersion1[i] > aVersion2[i]) {
            return 1;
        }  
    }
  
    return 0;
}

//检测Opera浏览器的版本
var isOpera = sUserAgent.indexOf("Opera") > -1;
var isMinOpera4 = isMinOpera5 = isMinOpera6 = isMinOpera7 = isMinOpera7_5 = false;
if (isOpera) {
    var fOperaVersion;
    if(navigator.appName == "Opera") {
        fOperaVersion = fAppVersion;     //Opera没有伪装的情况
    } else {
        var reOperaVersion = new RegExp("Opera (//d+//.//d+)");
        reOperaVersion.test(sUserAgent);
        fOperaVersion = parseFloat(RegExp["$1"]);       //利用正则表达式判断伪装之后的真正版本号
    }
    isMinOpera4 = fOperaVersion >= 4;
    isMinOpera5 = fOperaVersion >= 5;
    isMinOpera6 = fOperaVersion >= 6;
    isMinOpera7 = fOperaVersion >= 7;
    isMinOpera7_5 = fOperaVersion >= 7.5;
}
var isKHTML = sUserAgent.indexOf("KHTML") > -1
              || sUserAgent.indexOf("Konqueror") > -1
              || sUserAgent.indexOf("AppleWebKit") > -1;

//检测Safari浏览器的版本
var isMinSafari1 = isMinSafari1_2 = false;
var isMinKonq2_2 = isMinKonq3 = isMinKonq3_1 = isMinKonq3_2 = false;
if (isKHTML) {
    isSafari = sUserAgent.indexOf("AppleWebKit") > -1;
    isKonq = sUserAgent.indexOf("Konqueror") > -1;
    if (isSafari) {
        var reAppleWebKit = new RegExp("AppleWebKit///(//d+(?://.//d*)?)");
        reAppleWebKit.test(sUserAgent);
        var fAppleWebKitVersion = parseFloat(RegExp["$1"]);
        isMinSafari1 = fAppleWebKitVersion >= 85;
        isMinSafari1_2 = fAppleWebKitVersion >= 124;
    } else if (isKonq) {
        var reKonq = new RegExp("Konqueror///(//d+(?://.//d+(?://.//d)?)?)");
        reKonq.test(sUserAgent);
        isMinKonq2_2 = compareVersions(RegExp["$1"], "2.2") >= 0;
        isMinKonq3 = compareVersions(RegExp["$1"], "3.0") >= 0;
        isMinKonq3_1 = compareVersions(RegExp["$1"], "3.1") >= 0;
        isMinKonq3_2 = compareVersions(RegExp["$1"], "3.2") >= 0;
    }
  
}

//检测IE浏览器的版本
var isIE = sUserAgent.indexOf("compatible") > -1
           && sUserAgent.indexOf("MSIE") > -1
           && !isOpera;
         
var isMinIE4 = isMinIE5 = isMinIE5_5 = isMinIE6 = false;
if (isIE) {
    var reIE = new RegExp("MSIE (//d+//.//d+);");
    reIE.test(sUserAgent);
    var fIEVersion = parseFloat(RegExp["$1"]);
    isMinIE4 = fIEVersion >= 4;
    isMinIE5 = fIEVersion >= 5;
    isMinIE5_5 = fIEVersion >= 5.5;
    isMinIE6 = fIEVersion >= 6.0;
}

//检测Moz浏览器的版本
var isMoz = sUserAgent.indexOf("Gecko") > -1
            && !isKHTML;
var isMinMoz1 = sMinMoz1_4 = isMinMoz1_5 = false;
if (isMoz) {
    var reMoz = new RegExp("rv:(//d+//.//d+(?://.//d+)?)");
    reMoz.test(sUserAgent);
    isMinMoz1 = compareVersions(RegExp["$1"], "1.0") >= 0;
    isMinMoz1_4 = compareVersions(RegExp["$1"], "1.4") >= 0;
    isMinMoz1_5 = compareVersions(RegExp["$1"], "1.5") >= 0;
}

//检测NS4浏览器的版本
var isNS4 = !isIE && !isOpera && !isMoz && !isKHTML
            && (sUserAgent.indexOf("Mozilla") == 0)
            && (navigator.appName == "Netscape")
            && (fAppVersion >= 4.0 && fAppVersion < 5.0);
var isMinNS4 = isMinNS4_5 = isMinNS4_7 = isMinNS4_8 = false;
if (isNS4) {
    isMinNS4 = true;
    isMinNS4_5 = fAppVersion >= 4.5;
    isMinNS4_7 = fAppVersion >= 4.7;
    isMinNS4_8 = fAppVersion >= 4.8;
}

//平台/操作系统检测脚本
var isWin = (navigator.platform == "Win32") || (navigator.platform == "Windows");
var isMac = (navigator.platform == "Mac68K") || (navigator.platform == "MacPPC")
            || (navigator.platform == "Macintosh");
var isUnix = (navigator.platform == "X11") && !isWin && !isMac;
var isWin95 = isWin98 = isWinNT4 = isWin2K = isWinME = isWinXP = false;
var isMac68K = isMacPPC = false;
var isSunOS = isMinSunOS4 = isMinSunOS5 = isMinSunOS5_5 = false;
if (isWin) {
    isWin95 = sUserAgent.indexOf("Win95") > -1
              || sUserAgent.indexOf("Windows 95") > -1;
    isWin98 = sUserAgent.indexOf("Win98") > -1
              || sUserAgent.indexOf("Windows 98") > -1;
    isWinME = sUserAgent.indexOf("Win 9x 4.90") > -1
              || sUserAgent.indexOf("Windows ME") > -1;
    isWin2K = sUserAgent.indexOf("Windows NT 5.0") > -1
              || sUserAgent.indexOf("Windows 2000") > -1;
    isWinXP = sUserAgent.indexOf("Windows NT 5.1") > -1
              || sUserAgent.indexOf("Windows XP") > -1;
    isWinNT4 = sUserAgent.indexOf("WinNT") > -1
              || sUserAgent.indexOf("Windows NT") > -1
              || sUserAgent.indexOf("WinNT4.0") > -1
              || sUserAgent.indexOf("Windows NT 4.0") > -1
              && (!isWinME && !isWin2K && !isWinXP);
}
if (isMac) {
    isMac68K = sUserAgent.indexOf("Mac_68000") > -1
               || sUserAgent.indexOf("68K") > -1;
    isMacPPC = sUserAgent.indexOf("Mac_PowerPC") > -1
               || sUserAgent.indexOf("PPC") > -1;
}
if (isUnix) {
    isSunOS = sUserAgent.indexOf("SunOS") > -1;
    if (isSunOS) {
        var reSunOS = new RegExp("SunOS (//d+//.//d+(?://.//d+)?)");
        reSunOS.test(sUserAgent);
        isMinSunOS4 = compareVersions(RegExp["$1"], "4.0") >= 0;
        isMinSunOS5 = compareVersions(RegExp["$1"], "5.0") >= 0;
        isMinSunOS5_5 = compareVersions(RegExp["$1"], "5.5") >= 0;
    }
}