JS讀取UserAgent資訊並做判斷

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userAgent資訊可以由navigator.userAgent拿到。
例子：

<script type="text/javascript">    document.writeln("navigator.userAgent: " + navigator.userAgent + "<br />");    document.writeln("navigator.appName: " + navigator.appName + "<br />");    document.writeln("navigator.appCodeName: " + navigator.appCodeName + "<br />");    document.writeln("navigator.appVersion: " + navigator.appVersion + "<br />");    document.writeln("navigator.appMinorVersion: " + navigator.appMinorVersion + "<br />");    document.writeln("navigator.platform: " + navigator.platform + "<br />");    document.writeln("navigator.cookieEnabled: " + navigator.cookieEnabled + "<br />");    document.writeln("navigator.onLine: " + navigator.onLine + "<br />");    document.writeln("navigator.userLanguage: " + navigator.userLanguage + "<br />");    document.writeln("navigator.mimeTypes[1].description: " + navigator.mimeTypes[1].description + "<br />");    document.writeln("navigator.mimeTypes[1].type: " + navigator.mimeTypes[1].type + "<br />");    document.writeln("navigator.plugins[3].description: " + navigator.plugins[3].description + "<br />");</script>

如果想來判斷其中內容，可以用
navigator.userAgent.match()或navigator.userAgent.indexOf()來判斷
前者一般是用來判斷手機用戶端，例如navigator.userAgent.match(/iPhone/i) , navigator.userAgent.match(/Safari/i)
後者用來變向判斷userAgent字串中某值是否存在，例如 navigator.userAgent.indexOf("iPhone OS 4_0_2") !=-1

<script type="text/javascript">   var useHTML5 = 1;   if(navigator.userAgent.indexOf("iPhone OS 4_0_2") !=-1)   {      useHTML5=2;   }   document.write("Value is: <br>");   document.write(useHTML5);</script> 

所以它經常會用來判斷瀏覽器類型，如navigator.userAgent.indexOf("Firefox")>0