In this simple script i get the error "obj.parentNode.getElementById is not a function", and I have no idea, what is wrong.
<script type="text/javascript">
function dosomething (obj) {
sibling=obj.parentNode.getElementById("2");
alert(sibling.getAttribute("attr"));
}
</script>
<body>
<div>
<a id="1" onclick="dosomething(this)">1</a>
<a id="2" attr="some attribute">2</a>
</div>
</body>