代码示例:(标识:js_validation_html)
<!DOCTYPE html>
<html>
<body>

<h1>JavaScript 验证</h1>

<form action="/index/demo/form_current.html" 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>
运行结果: