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");