html中使用react，及ref操作

<!DOCTYPE html>
<html lang="en">
 
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
 
<body>
  <div id="app"></div>
</body>
</html>
  <script src="https://cdn.staticfile.org/react/16.4.0/umd/react.development.js"></script>
  <script src="https://cdn.staticfile.org/react-dom/16.4.0/umd/react-dom.development.js"></script>
  <script src="https://cdn.staticfile.org/babel-standalone/6.26.0/babel.min.js"></script>
  <script src="https://cdn.bootcss.com/prop-types/15.6.1/prop-types.js"></script>
  <script type="text/babel"> // 使用jsx语法
    class App extends React.Component {
      constructor (props) {
        super(props);
        this.state = {
          todoList: ['11', '22', '33']
        };
        this.addTodo = this.addTodo.bind(this)
      }
      addTodo (todo) {
        const {todoList} = this.state
        todoList.unshift(todo)
        this.setState({ todoList })
      }
      render() {
        const { todoList } = this.state;
        return (
          <div>
            Example
            <Add count={ todoList.length } addTodo={ this.addTodo }/>
            <List todoList={ todoList }/>
          </div>
        )
      }
    }
    class Add extends React.Component {

      constructor(props) {
        super(props);
        this.add = this.add.bind(this)
      }

      add() {
        const todo = this.todoInput.value.trim();
        if(!todo) return
        this.props.addTodo(todo)
        this.todoInput.value = ''
      }

      fnRef (input) {
        // 将 input元素 指定给todoInput
        return this.todoInput = input
      }

      render() {
        return (
          <div>
            {/* ref写法一 */}
            {/*
              <input type="text" ref={input => this.todoInput = input} />
            */}

            {/* ref写法二 */}
            <input type="text" ref={this.fnRef.bind(this)} />

            <button onClick={ this.add }>add #{this.props.count + 1}</button>
          </div>
        )
      }
    }

    Add.propTypes = {
      count: PropTypes.number.isRequired,
      addTodo:PropTypes.func.isRequired
    }

    class List extends React.Component {

      render() {
        const { todoList } = this.props
        return (
          <ul>
            {todoList.map((todo, key) => (<li key={key}>{todo}</li>))}
          </ul>
        )
      }

    }

    List.propTypes = {
      todoList: PropTypes.array.isRequired
    }
    
    ReactDOM.render(<App />, document.getElementById('app'));
  </script>
注意: react并不推荐过度使用ref，如果能通过state做到的事情，就不应该使用 refs 在你的 app 中“让事情发生”。
过度使用ref并不符合数据驱动的思想