使用onchange。试试这个
<div class="form-group" >
<label class="text-primary" dir="rtl" for="exampleFormControlSelect1">{{trans('admin.theplace')}}</label>
<select class="form-control" name="place" data-style="btn btn-link" id="exampleFormControlSelect1">
@foreach($places as $pt)
<option value="{{$pt->id}}" {{ ($pt->name)? "selected" : '' }} >{{$pt->name}} onchange="dropdown('{{$p->id}}')"</option>
@endforeach
</select>
</div>
<div class="form-group" >
<label class="text-primary" dir="rtl" for="exampleFormControlSelect1">{{trans('admin.itemCats')}}</label>
<select class="form-control" name="itemcat" id="category" data-style="btn btn-link" id="exampleFormControlSelect1">
@foreach($categories as $cat)
<option value="{{ $cat->id }}" {{ (isset($cat->name))? "selected" : '' }} >{{$cat->name}}</option>
@endforeach
</select>
</div>