<body>
<table border="1px" width="500px">
<tr>
<th>序号</th>
<th>姓名</th>
<th>年龄</th>
</tr>
<tbody id="hhh">
</tbody>
</table>
<script>
//问题
var tb = document.querySelector("tbody");
tb.innerHTML = "<tr><td>123</td><td>456</td><td>789</td></tr>";
</script>
</body>
效果图

<script>
//修改为有id获取元素
var but = document.getElementById("hhh");
but.innerHTML = "<tr><td>123</td><td>456</td><td>789</td></tr>"
</script>
效果图
