Sample Drupal BLOCK Code

function my_module_block($op = 'list', $delta = 0) {
  switch ($op) {
    case 'list':
      $block[0]['info'] = t('jQuery Hearbeat Test');
      return $block;
      break;
     
    case 'view':
      jquery_heartbeat_set(
        1500,
        'heartbeat-demo1',
        '',
        '$.my_script.percent_bar(\'heartbeat-demo2\'); 
         $.my_script.random_num(\'heartbeat-demo3\'); 
         $.my_script.random_clr(\'heartbeat-demo4\');',
        TRUE);
        
      $output  = '<div id="heartbeat-demo1">'
               .   t('Loading jQuery Hearbeat Test ...')
               . '</div>'
               . '<div id="heartbeat-demo2">'
               . '<table><tbody>'
               . '<tr>'
               .   '<td class="left">&nbsp;</td>'
               .   '<td class="right">&nbsp;</td>'
               . '</tr>'
               . '<tr><td class="percent" colspan="2">&nbsp;</td></tr>'
               . '</tbody></table>'
               . '</div>'
               . '<div id="heartbeat-demo3">'. t('Guessing ...') .'</div>';

      $block['subject'] = t('jQuery Hearbeat Test');
      $block['content'] = $output;
      
      return $block;
      break;
  }
}

Sample JavaScript Callback Code

_my_script_unique.counter = -1;
function _my_script_unique() {
  return _my_script_unique.counter++;
}
function _my_script_random(iMin, iMax) {
  return iMin + Math.floor(Math.random() * (iMax - iMin + 1));
}

$.my_script = {
  percent_bar: function(sID) {
    var iVal = _jheartbeat_unique() % 100;
    if (iVal < 1) iVal = 1;
    $('#'+ sID +' .left').css('width', iVal +'%');
    $('#'+ sID +' .right').css('width', (100 - iVal) + '%');
    $('#'+ sID +' .percent').html('<em>'+ iVal +'%</em>');
  },
  
  random_num: function(sID) {
    var iVal = _jheartbeat_random(1, 1000);
    $('#'+ sID).html('<span class="label">Magic number:</span> '+
                     '<span class="data">'+ iVal +'</span>');
  },
  
  random_clr: function(sID) {
    var iR = _jheartbeat_random(0, 255);
    var iG = _jheartbeat_random(0, 255);
    var iB = _jheartbeat_random(0, 255);
    $('#'+ sID).css('background-color', 'rgb('+ iR +','+ iG +','+ iG +')');
    $('#'+ sID).css('color', '#FFF');
  }
};