function loadcode() {
  var req = new XMLHttpRequest();
  if (req) {
    req.onreadystatechange = function() {
      if (req.readyState == 4 && (req.status == 200 || req.status == 304)) {
        removecode();
        var demo = document.getElementById('demo');
        demo.appendChild(document.createTextNode(req.responseText));
      }
    };
    req.open('GET', 'demo.js');
    req.send(null);
  }
}
function removecode() {
  var demo = document.getElementById('demo');
  while (demo.hasChildNodes()) {
    demo.removeChild(demo.firstChild);
  }
}