我目前有一个包含以下代码的表单，问题是当用户按下表单提交按钮时，即使没有检查必填字段，onclick呼叫仍然会被触发，我如何才能做到这一点，以便您必须完成必填字段在获得触发器之前？
<form method="post">
<div class="form-group">
<select id="inputState" class="form-control" style="width: 100%">
<option>10,000 credits</option>
<option>25,000 credits</option>
<option>50,000 credits</option>
<option>75,000 credits</option>
<option>100,000 credits</option>
</select>
</div>
<div class="text-center">
<div class="row justify-content-center mb-2">
<div class="col-12 col-md-8 text-center">
<p class="mb-0 small text-muted"><strong>Promotion Disclaimer</strong>
<br>You will be required to install a free mobile app from our sponsors to receive your Coins for free. This process only takes a minute or two and you can remove the app once you're finished.</p>
</div>
</div>
<div …