<body οnkeydοwn="check_key();" οnkeyup="up_key();" >
<script>
function up_key()
{
  var key_str = '.' + event.keyCode + '.';
  var reset_key = '.17.18.';
  
  if ( reset_key.indexOf(key_str) > -1)
  {
   window.key_alt_ctrl = null;
  }
  
  //alert(event.keyCode + ','+window.key_alt_ctrl);
}function check_key()
{
 
  switch(event.keyCode)
  {
    case 17://ctrl
      window.key_alt_ctrl = 'ctrl';
      break;
    case 18://alt
      window.key_alt_ctrl = 'alt';
      break;
    case 13://enter
      if (window.key_alt_ctrl == 'ctrl')
      {//按了ctrl+enter
        alert(1);
      }
      break;
    case 83://s
      if (window.key_alt_ctrl == 'alt')
      {//按了ctrl+enter
        alert(2);
      }
      break;
   default:
     window.key_alt_ctrl = null;
  }
  
}
</script>
</body>