[bes]

<script src="http://code.jquery.com/jquery-1.8.3.min.js"></script>
<style>
td {
	border: solid 1px gray;
	padding-left: 0.3em;
	padding-right: 0.3em;
	cursor: pointer;
}
</style>
<table>
	<tr>
		<td>1</td>
		<td>2</td>
		<td>3</td>
	</tr>
</table>
<script>
jQuery(function($){
	$('td').click(function() {
		var inputs = $(this).children("input");
		var text = $(this).text();
		var inp;
		if (inputs.length == 0) {
			inp = $(document.createElement("input")).attr("size", text.length).val(text);
			$(this).empty().append(inp);
			inp.focus();
			inp.on("blur", function () {
				$(this).parent().html($(this).val());
			});
		}
	});
});
</script>