How do I know if Javascript has been turned off inside browser?

<body>
...
...
<script type="text/javascript">
<!--
document.write("Hello World!")
//-->
</script>
<noscript>Your browser does not support JavaScript!</noscript>
...
...
</body>

<body>
...
...
<noscript>
    <iframe src ="/nojs.aspx?SOMEIDENTIFIER=XXXX&NOJS=TRUE" style="display: none;">
    </iframe>
</noscript>
...
...
</body>

<noscript>
    ...some non-js code
</noscript>

<script type="text/javascript" language="javascript">document.write("<input type='hidden' name='hasJs' value='1' />");