<button onclick="myFunction()">亲自试一试</button>
<!DOCTYPE html>
<html>
<head>
<style>
table,th,td
{
border:1px solid black;
}
</style>
</head>
<body>
<h3>演示如何访问 TH 元素</h3>
<table>
<tr>
<th id="myTh">名字</th>
</tr>
<td>乔布斯</td>
</table>
<p>点击按钮来改变 TH 元素的文本。</p>