Vit,
<menu type="context" id="cellpopup">
<menuitem label="Set NULL" onclick="SelNULL()"></menuitem>
</menu>
<table id="table" border="1">
<tr>
<td contextmenu="cellpopup">11111</td>
<td contextmenu="cellpopup">22222</td>
<td contextmenu="cellpopup">33333</td>
<tr>
</table>
<script>
var thisCell;
table.oncontextmenu = function(e) { thisCell = e.target };
function SelNULL() { alert(thisCell.innerHTML) }
</script>