JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>ToDoMvc</title>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
    <link rel="stylesheet" href="css/style.css">
    <script>
        function update(){
            $(document.getElementsByClassName('todos')).empty();
            $(document).ready(function () {
                $.get("/todos", function (data, status) {
                    var response = data.map(function (item) {
                        var li = document.createElement("li");
                        li.innerText = item.task;
                        if (item.completed == true) {
                            li.classList.add('done');
                            $('<input type="button" value="remove" />').prependTo(li);
                            $('<input type="checkbox" checked id="item.id" />').prependTo(li);
                        }
                        else {
                            li.classList.remove('done');
                            $('<input type="button" value="remove" />').prependTo(li);
                            $('<input type="checkbox" id="item.id" />').prependTo(li);
                        }
                        return li;
                    });

                    function writeToUl(selector, data) {
                        var ul = document.querySelector(selector);
                        response.forEach(function (item) {
                            ul.appendChild(item);
                        });
                    }

                    writeToUl(".todos", response)
                });
            });
        };
    </script>
</head>
<body onload="update()">
<ul class="todos" >

</ul>
<div class="newtodo">

    <script>
           function addToDo () {
            var todo = {task: $("#todotext").val()};
            var json = JSON.stringify(todo);
            $.ajax({
                type: "POST",
               ...