thinkphp5.0 select ajax

前端html

<select name="superlabel" id="superlabel">
    {volist name="allRes" id="vlabels"}
        <option value="{$vlabels.svid}">{$vlabels.svlabel}</option>
    {/volist}
</select>

前端js

<script>
$('#superlabel').change(function(){
    a=$(this).val();
    $.ajax({
        type:"POST",
        dataType:"json",
        url:"{:url('videosearch/label')}",
        data:'superlabel='+a,
        success:function(data){
            alert(data);
        },
        error:function(data){
            alert('none');
        }
    });
});
</script>

后端（PHP）

public function label(){
    return($_POST['superlabel']);
}