用JS改变表格中某一单元格的值。只有table有ID值

<table border=1 width=200 height=150 id='tab'>
<tr><td>111</td><td>111</td></tr>
<tr><td>222</td><td>222</td></tr>
<tr><td>333</td><td>333</td></tr>
<tr><td>444</td><td>444</td></tr>
</table>
<p align=center><input type='button' onclick='change()'>
<script>
function change(){
document.getElementById('tab').rows[0].childNodes[0].innerText = 'aaa';
}
</script>

 

 

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<table id="test">
<tr>
<td>hello</td>
</tr>
</table>
<script language="JavaScript">
alert(document.getElementById("test").rows[0].cells[0].innerText);
</script>