There are three problems:
- there is no innerHtml, innerHTML is the correct syntax.
- the hidden "p" does not have a value, it is not an input field. use innerHTML for accessing it.
- your javascript code runs before the browser knows about paragraps, so they don't exist when you want them to be accessed. put javascript after the paragraphs or run the code after the page is loaded.
this should work:
<html>
<head>
</head>
<body>
<p hidden="hidden" id="2">This paragraph should be hidden.</p>
<p>This is a visible paragraph.</p>
<p><b>Note:</b> The hidden attribute is not supported in IE.</p>
<p id="1"></p>
<script type="text/javascript">
var x= document.getElementById("2").innerHTML;
document.getElementById("1").innerHTML = x;
</script>
</body>
</html>