[bes]

<table id="table">
	<tr>
		<td>1</td>
		<td>2</td>
	</tr>
</table>
<button id="but">save</button>
<script>
window.onload = function () {
	but.onclick = function () {
		window.open("data:application/vnd.ms-excel," + table.outerHTML);
	}
}
</script>

не, первое чёт не прокатило

<div id="div">
	<table>
		<tr>
			<td>1</td>
			<td>2</td>
		</tr>
	</table>
</div>
<button id="but">save</button>
<script>
window.onload = function () {
	but.onclick = function () {
		window.open("data:application/vnd.ms-excel," + div.innerHTML);
	}
}
</script>