jQuery addClass example

Change class name on click in jQuery

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<form method="POST">
Número de série: <input type="text" id="numeroSerie" required><br>
<br>Usuário: <input type="text" id="user" required><br>
<br>Senha: <input type="password" id="pass" required><br>
<br><input type="submit" id="enter">
</form>

JavaScript

$(document).ready(function () {
  $("#enter").on("click", function () {
		$("input:required").each(function(){
    	var _$this = $(this);
    	_$this.val(_$this.val() == "" ? "" : _$this.val);
    });
  });
});