$request->ajax() is not working

Quiz app, laravel 5.2, I am making a ajax request for a search form and I want to check if it's an ajax request versus a form submit so I'm testing with

QuizController.php

        public function search(Request $request){

    if($request->wantsJson()){
            dd("it wanted json");
        }
        else{
            dd("it didn't want json");
        }

        if ($request->ajax()) {
            dd("its ajax");
        }
        else{
            dd("its not ajax");
        }

    

        $query = $request->get('query');

        $results = Quiz::where('title',$query)->get();

        return response()->json($results);
    }

But the ajax() or wantsJson() are not being triggered, but the ajax calls were going thru

        $('#query').on('keyup', function() {

             if (this.value.length > 1) {
                  $.ajax({
                      type:"POST",
                      url:"quiz/search",
                      data:$("#searchForm").serialize(),
                      success:function(data){
                          console.log(data);

                          $('#results').removeAttr('hidden');

                          for(var key in data){

                  $("#results").prepend("<li><a href='{{route('quiz.show',['id' =>" + data[key].id + " ])}}' >" + data[key].title + "</a></li>");
                          }
                      }
                  });
             }
        });

form

        <form class="navbar-form navbar-left"  id="searchForm" method="post" action="{{route('quiz.search')}}">
                        {{ csrf_field() }}
                       <div class="form-group">
                         <input type="text" id="query" class="form-control" name="query" placeholder="Search">
                         <ul id="results" hidden>

                         </ul>
                       </div>
                       <button id="searchSubmit" type="submit" class="btn btn-default">Submit</button>
                    </form>

I have tried adding the

use Request; in addition to the use Illuminate\Http\Request; at the beginning of the Quiz controller file