select的onchange方法获得value值

<select class="aa" onchange="select-plat()">

          <option value="">板式选择</option>

          <option value="1">列表展示</option>

          <option value="2">两列</option>

          <option value="3">大图显示</option>

</select>

js代码

<script>

    function select-plat(){

        var val = $(".aa").val();

        

    }

</script>