如何在slideUp时添加css类并在slideDown时添加css类?
$("#hide_top").click(function () {
$("#hide_top").addClass();
$("#formdate").slideUp();
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
&#13;
$("#hide_top").click(function () {$("#formdate")});