var halloween = parseInt(document.getElementById('time_until_halloween').innerHTML);
var christmas = parseInt(document.getElementById('time_until_christmas').innerHTML);

function countdown(div, text)
 {
 halloween--;
 christmas--;
 if (halloween > 0)
  document.getElementById('time_until_halloween').innerHTML = halloween + ' seconds until next Halloween';
 else
  document.getElementById('time_until_halloween').innerHTML = 'This is Halloween!';
 if (christmas > 0)
  document.getElementById('time_until_christmas').innerHTML = christmas + ' seconds until next Christmas';
 else
  document.getElementById('time_until_christmas').innerHTML = 'It\'s Christmas-time!';
 }
 
window.setInterval('countdown()', 1000);