<html>
<body>
<form action="form_action.asp">
Homepage: <input type="url" id="myURL" name="website">
<input type="submit" value="提交">
</form>
<p>点击 "点我" 按钮设置 URL 字段的 required 属性。</p>
<p><strong>提示:</strong> 在点击 “点我” 按钮前后点击 "提交" 按钮查看效果</p>
<button onclick="myFunction()">点我</button>
<p id="demo"></p>
<script>
function myFunction() {
document.getElementById("myURL").required = true;
document.getElementById("demo").innerHTML = "required 属性已设置。表单提交前 URL 字段为必填字段。";
}
</script>
</body>
</html>