使用iOS 4.3到6.0.1和Android 2.3.4到4.2的实际用户代理字符串进行测试

var userOS;    // will either be iOS,Android or unknown
var userOSver; // this is a string,use Number(userOSver) to convert

function getOS( )
{
  var ua = navigator.userAgent;
  var uaindex;

  // determine OS
  if ( ua.match(/iPad/i) || ua.match(/iPhone/i) )
  {
    userOS = 'iOS';
    uaindex = ua.indexOf( 'OS ' );
  }
  else if ( ua.match(/Android/i) )
  {
    userOS = 'Android';
    uaindex = ua.indexOf( 'Android ' );
  }
  else
  {
    userOS = 'unknown';
  }

  // determine version
  if ( userOS === 'iOS'  &&  uaindex > -1 )
  {
    userOSver = ua.substr( uaindex + 3,3 ).replace( '_','.' );
  }
  else if ( userOS === 'Android'  &&  uaindex > -1 )
  {
    userOSver = ua.substr( uaindex + 8,3 );
  }
  else
  {
    userOSver = 'unknown';
  }
}

然后要检测特定版本和更高版本,请尝试：

if ( userOS === 'iOS' && Number( userOSver.charAt(0) ) >= 5 ) { ... }