Unexpected token A in JSON at position 0?

web.php

Route::post('portal/student_exam_info_edit','PortalOperation@student_exam_info_edit');

Controller its my portaloperation controller and i want to show data in request but i show error

  public function student_exam_info_edit(Request $request)
    {
             print_r($request->all());
    }

student_exam_info.blade.php

@extends('layouts.portal')
@section('title','Exam Form')
@section('content')
    <!-- Content Wrapper. Contains page content -->
    <div class="content-wrapper">
        <!-- Content Header (Page header) -->
        <div class="content-header">
            <div class="container-fluid">
                <div class="row mb-2">
                    <div class="col-sm-6">
                        <h1 class="m-0 text-dark">Student Exams Info</h1>
                    </div><!-- /.col -->
                    <div class="col-sm-6">
                        <ol class="breadcrumb float-sm-right">
                            <li class="breadcrumb-item"><a href="#">Home</a></li>
                            <li class="breadcrumb-item active">Student Exams Info</li>
                        </ol>
                    </div><!-- /.col -->
                </div><!-- /.row -->
            </div><!-- /.container-fluid -->
        </div>
        <!-- /.content-header -->
        <section class="content">
            <div class="container-fluid">
                <div class="row">
                    <div class="col-12">
                        <!-- Default box -->
                        <div class="card">
                            <div class="card-body">
                                <div class="row">
                                    <div class="col-sm-6">
                                        <h3> </h3>
                                    </div>
                                    <div class="col-sm-6">
                                        <h3> <span class="float-right"></span></h3>
                                    </div>
                                </div>
                                <form action="" class="database_operation">
                                    <div class="row">
                                        <div class="col-sm-12">
                                            <div class="form-group">
                                                <label>Enter Name</label>
                                                
                                                <input type="hidden" name="id" value="">
                                                <input type="text" name="name" required="required" value="" placeholder="Enter Name" class="form-control">
                                            </div>
                                        </div>
                                        <div class="col-sm-12">
                                            <div class="form-group">
                                                <label>Enter E-Mail</label>
                                                <input type="text" required="required" name="email" value="" placeholder="Enter E-Mail" class="form-control">
                                            </div>
                                        </div>
                                        <div class="col-sm-12">
                                            <div class="form-group">
                                                <label>Enter Mobile No</label>
                                                <input type="text" name="mobile_no" value="" placeholder="Enter Mobile No" class="form-control">
                                            </div>
                                        </div>
                                        <div class="col-sm-12">
                                            <div class="form-group">
                                                <label>Select DOB</label>
                                                <input type="date" name="dob" value=""  class="form-control">
                                            </div>
                                        </div>
                                        <div class="col-sm-12">
                                            <div class="form-group">
                                                <label>Enter Password</label>
                                                <input type="password" name="password"   placeholder="Enter Password" class="form-control">
                                            </div>
                                        </div>
                                        <div class="col-sm-12">
                                            <div class="form-group">
                                                <button class="btn btn-info"> Update</button>
                                            </div>
                                        </div>
                                    </div>
                                </form>
                            </div>

                            <!-- /.card-body -->

                            <!-- /.card-footer-->
                        </div>
                        <!-- /.card -->
                    </div>
                </div>
            </div>
        </section>
    </div>
@endsection

custom.js

$(document).on('submit','.database_operation',function () {
    var url=$(this).attr('action');
    var data=$(this).serialize();
    $.post(url,data,function (fb) {
             var resp=$.parseJSON(fb)
        if(resp.status=='true')
        {
           alert(resp.message) ;
           setTimeout(function () {
               window.location.href = resp.reload;
           },1000);
           }
           else
        {
            alert(resp.message) ;
        }
    })
    return false;
});
$(document).on('click','.category_status',function () {
var id=$(this).attr('data-id');
$.get(BASE_URL+'/admin/category_status/'+id,function (fb) {
    alert('Status Successfully Changed');
})
});
$(document).on('click','.exam_status',function () {
    var id=$(this).attr('data-id');
    $.get(BASE_URL+'/admin/exam_status/'+id,function (fb) {
        alert('Status Successfully Changed');
    })
});
$(document).on('click','.student_status',function()
{
    var id=$(this).attr('data-id');
    $.get(BASE_URL+'/admin/student_status/'+id,function (fb) {
        alert('Status Successfully Changed');
    })
})
$(document).on('click','.portal_status',function()
{
    var id=$(this).attr('data-id');
    $.get(BASE_URL+'/admin/portal_status/'+id,function (fb) {
        alert('Status Successfully Changed');
    })
})

Error When i update form and check inspect element network i cant understand what is this error means how to it solve i find solution couple of hours but cant solve

VM2391:1 Uncaught SyntaxError: Unexpected token A in JSON at position 0
    at Function.parse [as parseJSON] (<anonymous>)
    at Object.success (custom.js:5)
    at c (jquery.min.js:2)
    at Object.fireWith [as resolveWith] (jquery.min.js:2)
    at l (jquery.min.js:2)
    at XMLHttpRequest.<anonymous> (jquery.min.js:2)
(anonymous) @ custom.js:5
c @ jquery.min.js:2
fireWith @ jquery.min.js:2
l @ jquery.min.js:2
(anonymous) @ jquery.min.js:2
load (async)
send @ jquery.min.js:2
ajax @ jquery.min.js:2
k.<computed> @ jquery.min.js:2
(anonymous) @ custom.js:4
dispatch @ jquery.min.js:2
v.handle @ jquery.min.js:2

via Chebli Mohamed