Todo.tsx

import React, { Component } from 'react';
import { observer } from 'mobx-react/index';
import { observable } from 'mobx/lib/mobx';

@observer
export class Todo extends Component<{todoId: string}, {}> {
 
  @observable
  private todo: Todo;
 
  async componentWillMount () {
    const { todoId } = this.props;
    this.todo = await fetch(`http://.../${todoId}`);
  }
 
  render() {
    if(this.todo != null) {
      return (
        <p>{this.todo.name} <button onClick={() => this.todo.active = true}>activate</button></p>
      );
    }
  }
}