React Base Fiddle (JSX)

Starting point for creating JSFiddles with React.

HTML

<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<div id="app">
    <!-- This element's contents will be replaced with your component. -->
</div>

Babel + JSX

class ToDo extends React.Component {
  constructor() {
    super()
    this.state = {
      todos: [],
      inputValue: null
    }
    this.changeValue = this.changeValue.bind(this)
    this.addTodo = this.addTodo.bind(this)
    this.removeTodo = this.removeTodo.bind(this)
  }

  changeValue(e) {
    this.setState({inputValue: e.target.value})
  }

  addTodo(e) {
    e.preventDefault()

    const newTodoItem = {
      id: Date.now(),
      inputValue: this.state.inputValue
    }

    if(!this.state.inputValue.length) return

    this.setState(state => ({
      todos: state.todos.concat(newTodoItem),
      inputValue: ''
    }))
  }

  removeTodo(e) {
  
    const et = e.target
    const attr = et.getAttribute("data-key");

    this.setState(state => ({
      todos: state.todos.filter(item => item.id != attr)
    }))
  }

  render() {
    return(
      <div>
        <form onSubmit={this.addTodo}>
          <input
            type='text'
            name='todo'
            placeholder='Enter a ToDo'
            value={this.state.inputValue}
            onChange={this.changeValue}
          />
          <input type='submit' value='Add' />
          &nbsp;&nbsp;&nbsp;
          <span>ToDos: {this.state.todos.length}</span>
        </form>
        <TodoList items={this.state.todos} itemClickEvent={this.removeTodo} />
      </div>
    )
  }
}

class TodoList extends React.Component {
  render() {
    const items = this.props.items
    return(
      <ul>
        {
          items.map(item => (
            <li key={item.id} data-key={item.id} onClick={this.props.itemClickEvent}>{item.inputValue}</li>
          ))
        }
      </ul>
    )
  }
}

ReactDOM.render(<ToDo />, document.querySelector('#app'))