laravel undefine variable : category

Please help me; I am new to Laravel, and I'm not getting what I'm doing wrong.

Here is my view:

    <div class="container">
    <h1>category and subcategory</h1>
    <div class="row">
    <div class="col-md-10 col-md-offset-1">
    {!! Form::open(array('url' => '','files'=>true))  !!}
    {!! Form::token(); !!}
     <div class="form-group">
     <label for="">category</label>
     <select class="form-control input-sm" name="" id="">
       @foreach ( $category as $category) 
       <option value=""></option>
        @endforeach
         </select>
          </div>                    
         <div class="form-group">
         <label for="">subcategory</label>
         <select class="form-control input-sm" name="" id="" >
         <option value=""></option>
          </select>
            </div>
            </form>
             </div>
              </div>
       <script type="text/javascript">
       $(document).ready(function() {
       $("#category").on('change',function(e) {
       console.log(e);
       var cat_id = e.target.value;
       $.get('/ajax-subcat/' + cat_id , function(data){
        //success data
        console.log(data);
        })
       });
       </script>
         </div>    
            </div>
                </div>  

Here is my route:

       Route::get('/', function () {
       $category=\App\category::all();
       return view('layouts.app')->with ('categories',$category);
           });
          Route::get('/ajax-subcat',function(){
             $category=\App\category::all();
               $cat_id = Input::get('cat_id');
         $subcategory = subcategory::where('category_id', '=', $cat_id)
                      ->orderBy('name', 'asc')
                      ->get();
                return response()->json($subcategory);
         });

And this is my error log file:

ErrorException in ec195dc7ec967851481b4815c28c6879244d5d45.phpline 87: Undefined variable: category(View: C:\xampp\htdocs\laravel\resources\views\layouts\app.blade.php) (View: C:\xampp\htdocs\laravel\resources\views\layouts\app.blade.php) in ec195dc7ec967851481b4815c28c6879244d5d45.php line 87 at CompilerEngine->handleViewException(object(ErrorException), '1') in PhpEngine.php line 44 at PhpEngine-

What is causing these errors?

via Bipin Shukla