function doLoad(value)
{
  // Create new JsHttpRequest object.
  var req = new JsHttpRequest();
  // Code automatically called on load finishing.
  req.onreadystatechange = function()
  {
    if (req.readyState == 4)
    {
      // Write result to page element ($_RESULT become responseJS).
      document.getElementById('music_cat').innerHTML = req.responseJS.out_str;
      // Write debug information too (output become responseText).
//      document.getElementById('debug').innerHTML = req.responseText;
    }
  }
  // Prepare request object (automatically choose GET or POST).
  req.open(null, 'index_ajax.php', true);
  // Send data to backend.
  req.send( { q: value } );
}