<!DOCTYPE html>
<html>
<body>
<h1>JavaScript 验证</h1>
<form action="/demo/html/action_page.php" method="post">
<input type="text" name="fname" required>
<input type="submit" value="提交">
</form>
<p>如果您点击提交，而不填写文本字段，浏览器将显示错误消息。</p>
</body>
</html>