<script>

  var os = function() {

  var ua = navigator.userAgent, //获取浏览器UA

  isWindowsPhone = /(?:Windows Phone)/.test(ua),

  isSymbian = /(?:SymbianOS)/.test(ua) || isWindowsPhone,

  isAndroid = /(?:Android)/.test(ua),

  isFireFox = /(?:Firefox)/.test(ua),

  isChrome = /(?:Chrome|CriOS)/.test(ua),

  isTablet = /(?:iPad|PlayBook)/.test(ua) || (isAndroid && !/(?:Mobile)/.test(ua)) || (isFireFox && /(?:Tablet)/.test(ua)),

  isPhone = /(?:iPhone)/.test(ua) && !isTablet,

  isPc = !isPhone && !isAndroid && !isSymbian;

  return {

    isTablet: isTablet,

    isPhone: isPhone,

    isAndroid : isAndroid,

    isPc : isPc

  };

}();

if(os.isPc) //判断是否PC

  alert("PC");

else if(os.isPhone) //判断是否iPhone

  alert("Phone");

else if(os.isAndroid) //判断是否Android

  alert("Android");

else if(os.isTablet) //判断是否平板

  alert("Tablet");

</script>