JSデータがしっかりと保存できるにしたいです

前提・実現したいこと

laravelとJavaScriptsでTodoリストの管理システムを作っています。
Todolistの部分を保存更新出来るようにしたいと考えています。
TodolistはJavaScritsのみのため、保存できるようにテーブルを作成しました。
その後保存するための記述をコントローラーに記述した際に以下のエラーメッセージが発生しました。

発生している問題・エラーメッセージ

Failed to load resource: the server responded with a status of 500 (Internal Server Error)

該当のソースコード

Migration
1<?php
2
3use Illuminate\Database\Migrations\Migration;
4use Illuminate\Database\Schema\Blueprint;
5use Illuminate\Support\Facades\Schema;
6
7class Todolist extends Migration
8{
9    /**
10     * Run the migrations.
11     *
12     * @return void
13     */
14    public function up()
15    {
16        Schema::create('todolists', function (Blueprint $table) { 
17            $table->integer('id')->autoIncrement(); 
18            $table->integer('user_id');
19            $table->string('content'); 
20            $table->timestamps(); 
21        }); 
22        //
23    }
24
25    /**
26     * Reverse the migrations.
27     *
28     * @return void
29     */
30    public function down()
31    {
32        //
33    }
34}
35
36

Model
1<?php
2
3namespace App;
4
5use Illuminate\Database\Eloquent\Model;
6use Illuminate\Database\Eloquent\Relations\BelongsTo;
7
8class Todolist extends Model
9{
10    public function user(): BelongsTo
11    {
12        return $this->belongsTo('App\User');
13    }
14    //
15}
16

Controller
1<?php
2
3namespace App\Http\Controllers;
4
5use Illuminate\Http\Request;
6use App\Todolist;
7
8class TodoController extends Controller
9{
10    public function index()
11    {
12        $todolist = Todolist::orderBy('id', 'content')->get();
13
14        return view('todolist.index',[
15        'todolists' => $todolist
16        ]);        
17    }
18
19    public function register(Request $request){
20            $todolist = new Todolist;
21            $todolist->todolist = $request->todolist;
22            $todolist->save();
23            return redirect('/');
24    }
25}
26

Routes
1<?php
2
3use Illuminate\Support\Facades\Route;
4
5
6Auth::routes();
7
8Route::get('/home', 'HomeController@index')->name('home');
9
10Route::group(['middleware' => ['auth']], function(){
11Route::get('/','Todocontroller@index');
12Route::post('/register', 'Todocontroller@@register');
13Route::get('/holiday','CalendarController@getHoliday');
14Route::post('/holiday','CalendarController@postHoliday');
15Route::get('/show','CalendarController@show');
16Route::get('/holiday/{id}','CalendarController@getHolidayId');
17Route::delete('/holiday','CalendarController@deleteHoliday');
18
19});
20
21

view
1<!DOCTYPE html>
2<html lang="ja">
3  <head>
4    <meta charset="UTF-8" />
5    <meta name="viewport" content="width=device-width, initial-scale=1" />
6
7    <title>kanrin</title>
8    <link rel="stylesheet" href="../css/jkanban.min.css" />
9    <link
10      href="https://fonts.googleapis.com/css?family=Lato"
11      rel="stylesheet"
12    />
13
14    <style>
15      body {
16        font-family: "Lato";
17        margin: 0;
18        padding: 0;
19      }
20
21      #myKanban {
22        overflow-x: auto;
23        padding: 20px 0;
24      }
25
26      .success {
27        background: #00b961;
28      }
29
30      .info {
31        background: #2a92bf;
32      }
33
34      .warning {
35        background: #f4ce46;
36      }
37
38      .error {
39        background: #fb7d44;
40      }
41    </style>
42  </head>
43  <body>
44  @extends('layout')
45<div id="app">
46        <nav class="navbar navbar-expand-md navbar-light bg-white shadow-sm">
47            <div class="container">
48                <a class="navbar-brand" href="{{ url('/') }}">
49                    {{ config('app.name', 'Laravel') }}
50                </a>
51                <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="{{ __('Toggle navigation') }}">
52                    <span class="navbar-toggler-icon"></span>
53                </button>
54
55                <div class="collapse navbar-collapse" id="navbarSupportedContent">
56                    <!-- Left Side Of Navbar -->
57                    <ul class="navbar-nav mr-auto">
58
59                    </ul>
60
61                    <!-- Right Side Of Navbar -->
62                    <ul class="navbar-nav ml-auto">
63                        <!-- Authentication Links -->
64                        @guest
65                            <li class="nav-item">
66                                <a class="nav-link" href="{{ route('login') }}">{{ __('Login') }}</a>
67                            </li>
68                            @if (Route::has('register'))
69                                <li class="nav-item">
70                                    <a class="nav-link" href="{{ route('register') }}">{{ __('Register') }}</a>
71                                </li>
72                            @endif
73                        @else
74                            <li class="nav-item dropdown">
75                                <a id="navbarDropdown" class="nav-link dropdown-toggle" href="#" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" v-pre>
76                                    {{ Auth::user()->name }}
77                                </a>
78
79                                <div class="dropdown-menu dropdown-menu-right" aria-labelledby="navbarDropdown">
80                                    <a class="dropdown-item" href="{{ route('logout') }}"
81                                       onclick="event.preventDefault();
82                                                     document.getElementById('logout-form').submit();">
83                                        {{ __('Logout') }}
84                                    </a>
85
86                                    <form id="logout-form" action="{{ route('logout') }}" method="POST" class="d-none">
87                                        @csrf
88                                    </form>
89                                </div>
90                            </li>
91                        @endguest
92                    </ul>
93                </div>
94            </div>
95        </nav>
96
97        <main class="py-4">
98            @yield('content')
99        </main>
100    </div>
101    <div id="myKanban"></div>
102    <!-- 導入予定機能 -->
103    <!-- <button id="addDefault">Add "Default" board</button>
104    <br />
105    <button id="addToDo">Add element in "To Do" Board</button>
106    <br />
107    <button id="removeElement">Remove "My Task Test"</button> -->
108    <script src="../js/jkanban.js"></script>
109    <script>
110      var KanbanTest = new jKanban({
111        element: "#myKanban",
112        gutter: "10px",
113        widthBoard: "450px",
114        itemHandleOptions:{
115          enabled: true,
116        },
117        
118        click: function(el) {
119
120        },
121        dropEl: function(el, target, source, sibling){
122  
123        },
124        buttonClick: function(el, boardId) {
125
126          // create a form to enter element
127          var formItem = document.createElement("form");
128          formItem.setAttribute("class", "itemform");
129          formItem.innerHTML =
130            '<div class="form-group"><textarea class="form-control" rows="2" autofocus></textarea></div><div class="form-group"><button type="submit" class="btn btn-primary btn-xs pull-right">作成</button><button type="button" id="CancelBtn" class="btn btn-danger btn-xs pull-right">取消</button></div>';
131
132          KanbanTest.addForm(boardId, formItem);
133          formItem.addEventListener("submit", function(e) {
134            e.preventDefault();
135            var text = e.target[0].value;
136            KanbanTest.addElement(boardId, {
137              title: text
138            });
139            formItem.parentNode.removeChild(formItem);
140          });
141          document.getElementById("CancelBtn").onclick = function() {
142            formItem.parentNode.removeChild(formItem);
143          };
144        },
145        addItemButton: true,
146        boards: [
147          {
148            id: "_todo",
149            title: "To Do",
150            class: "info,good",
151            dragTo: ["_working"],
152            item: [
153
154            ]
155          },
156          {
157            id: "_working",
158            title: "Working ",
159            class: "warning",
160            item: [
161        
162            ]
163          },
164          {
165            id: "_done",
166            title: "Done ",
167            class: "success",
168            dragTo: ["_working"],
169            item: [
170              
171            ]
172          }
173        ]
174      });
175      var removeBoard = document.getElementById("removeBoard");
176      removeBoard.addEventListener("click", function() {
177        this.remove();
178      },false);
179
180    </script>
181    <a href="{{ url('/holiday') }}" class="todo-btn">予定入力画面へ</a>
182    
183  </body>
184</html>
185