markering af mange checkboxes

Noget i den her stil?:

<form name="FORMNAVN">
  <input type="checkbox" name="ting[]">
  <input type="checkbox" name="ting[]">
  <input type="checkbox" name="ting[]">
  <input type="checkbox" name="ting[]">
  <input type="checkbox" name="ting[]">
</form>

<img src="1.gif" onclick="java script:mark()">

<script type="text/JavaScript">
function mark()
{
el = document.FORMNAVN.elements;
for (i=0; i < el.length; i++) {
  if (el[i].type == "checkbox") { el[i].checked = true }
}
}
</script>

Yes, svar

Svar! :)

Takker for point! :)