如何防止按钮在未选择值时提交表单.不使用javascript - How to prevent buttons from submitting forms when value is not selected. Without using javascript

How to prevent buttons from submitting forms when value is not selected. Without using javascript

在不使用javascript的情况下，是否可以在未选择值时阻止按钮提交表单？

这是我的代码。

<!-- form -->
<form name="aform" action="second_page.php" method="POST">
    <div id="collegelane">
         Please choose only one from the following rooms:
    </div>
    <?php
         // connects to database
         require("user_connection.php");

         $q = mysqli_query($connect, "SELECT * FROM `campus`");
         while ($line = mysqli_fetch_assoc($q)) {
         echo '<input id="onclick" type="checkbox" name="car" 
            value="'.$line['room'].'"><label>'.$line['room'].'</label></br>';
        }
    ?>
    </br>
    </br>
    <div id="next">
        <input type="submit" name="next" Value="next"/>
    </div>
</form>

因为已经建议在复选框上添加一个"必需"属性，如下所示，它应该可以工作。不确定浏览器对该属性的支持，我怀疑它可能不适用于某些版本的 IE。

<?php
             // connects to database
             require("user_connection.php");

             $q = mysqli_query($connect, "SELECT * FROM `campus`");
             while ($line = mysqli_fetch_assoc($q)) {
             echo '<input id="onclick" required type="checkbox" name="car" 
                value="'.$line['room'].'"><label>'.$line['room'].'</label></br>';
            }
        ?>

html5 表单验证：http://www.the-art-of-web.com/html/html5-form-validation/

AngularJs 表单验证：https://docs.angularjs.org/guide/forms