Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd">
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
</head>
<body>
<table id="mytable" cellpadding="0" cellspacing="0" border="1" width="960">
<tr>
<td width="100">Jons</td>
<td>Web Developer</td>
</tr>
<tr>
<td width="100">Thomas</td>
<td>Web Developer</td>
</tr>
<tr>
<td width="100">Dijomon</td>
<td>Java Developer</td>
</tr>
</table>
<script type="text/javascript">
(function(){
var thc=document.getElementById('mytable').rows[0].cells;
var newth;
for (var i_tem = 0; i_tem < thc.length; i_tem++){
newth=document.createElement('th');
newth.innerHTML=thc[i_tem].innerHTML;
thc[i_tem].parentNode.replaceChild(newth, thc[i_tem]);
}
})();
</script>
</body>
</html>
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