raf2205 on "access my footer using javascript in a .php file"

Hi,
I am trying to access my footer using javascript in a .php file.
but the footer var is always null.
any help?

<script type="text/javascript">
  var _document = jQuery(document);
  var footer = document.getElementById("colophon");
  console.log("footer: " + footer);

  //footer.style.marginRight = 100 + 'px';

</script>