​x
 
<html>
<head>
<base id="myBaseId" href="https://www.w3school.org.cn/htmldom/" />
</head>
​
<body>
​
<p>Base id: 
<script type="text/javascript">
x=document.getElementsByTagName('base')[0];
document.write(x.id);
</script></p>
​
</body>
​
</html>
​