index.js

import React from 'react';
import ReactDOM from 'react-dom';
import * as mobx from 'mobx';
import mobxReact from 'mobx-react';
import remotedev from 'mobx-remotedev/lib/dev';

mobx.useStrict(true);
var todoFactory = function (title) {

  var todo = {
    id: Math.random(),
    toggleStatus: mobx.action(function toggleStatus() {
      todo.finished = !todo.finished;
    })
  };
  mobx.extendObservable(todo,
    {
      title: title,
      finished: false
    }
  );
  return todo;
};

var todoListFactory = function () {
  var todoList = {
    addTodo: mobx.action(function addTodo (todo) {
      todoList.todos.push(todoFactory(todo));
    }),
    addTodos: mobx.action(function addTodos (todos) {
      todoList.todos = todoList.todos.concat(todos.map(todo => todoFactory(todo)));
    })
  };

  mobx.extendObservable(todoList, {
    todos: [],
    unfinishedTodoCount: function () {
      return todoList.todos.filter(function (todo) {
        return !todo.finished;
      }).length;
    }
  });

  return remotedev(todoList, { name: 'Todo list', global: true });
};

var TodoListView = mobxReact.observer(function TodoListView() {
    var listItems = this.props.todoList.todos.map(function (todo) {
      return React.createElement(TodoView, {todo: todo, key: todo.id});
    });

    return React.createElement('div', null,
      React.createElement('ul', null, listItems),
      'Tasks left: ' + this.props.todoList.unfinishedTodoCount
    );
  }
);

var TodoView = mobxReact.observer(
  React.createClass({
    displayName: 'TodoView',
    render: function () {
      var todo = this.props.todo;
      return React.createElement('li', null,
        React.createElement('input', {
          type: 'checkbox',
          checked: todo.finished,
          onClick: this.selectHandler
        }),
        todo.title
      );
    },
    selectHandler: function () {
      this.props.todo.toggleStatus();
    }
  })
);

var store = todoListFactory();

ReactDOM.render(
  React.createElement(TodoListView, {todoList: store}),
  document.getElementById('root')
);

store.addTodos(['Get Coffee', 'Write simpler code']);
store.todos[0].toggleStatus(true);