Textfeldeingabe per checkbox ändern

[Peter]

Des sollte gehen:
<script type="text/javascript">
function setid() {

if(document.add.autoip.getAttribute('checked')==false)
document.add.onoff.setAttribute('value', 'on');

if(document.add.autoip.getAttribute('checked')==true)
document.add.onoff.setAttribute('value', 'off');

}
</script>

<form name="add" action="" method="get">

<input name="onoff" type="text">

<input name="autoip" type="checkbox" value="1" onpropertychange="setid()"> on / off
</form>

mfg Peter