the value of variable in javascrip and jquery doesnt show

I recently learn how to code in js and jquery and im confused ,why value of variable a doesn't show? I think it should be 1 or 0 depend on value inside of variable bayar, but why its doesn't work

ive tried to do anything that I can do but it doesn't work like it try to change several code but it doesn't work

heres my controller code

 public function generated(){
 $data=DB::table("tb_trx_perhitungan_bunga_simpanan")
        ->selectRaw('trx_bulan')
        ->get();  

  return view('crud.form.cobaNampilin',compact('data'));
 }

and heres my javascript and jquery code

<script src="//code.jquery.com/jquery-3.3.1.min.js"></script>
        <script type="text/javascript">
        $(document).ready(function() {
            var a;
            var array = {!! json_encode($data) !!};
            var i;
            var b;
            $('#bulan').keyup(function(){
            var bayar=parseInt($('#bulan').val());
                for(i=0;i<=array.length;i++){
                    if(bayar==array[i].trx_bulan){
                        a=1;
                    }
                    else{
                        a=0;
                    }
                }

             $('#hasil').val(a);
            });
        });
        </script>

I expected the output is 1 or 0

strong text

via Chebli Mohamed