How to get any element of Webpage

<html>

<head>

<script type="text/javascript">

function getElement()

{

var x=document.getElementById("myHeader");

alert("I am a " + x.tagName + " element");

}

</script>

</head>

<body>

<h1 id="myHeader" onclick="getElement()">Click to see what element I am!

</h1>

</body>

</html>