class CustomTextInput extends React.Component {
   constructor(props) {
      super(props);
      this.textInputRef = React.createRef();
   }
   focusTextInput() {      // (1) accessing method of DOM node
      this.textInputRef.current.focus();
   }
   render() {
      return (<input type="text" ref={this.textInputRef} />);
   }}class AutoFocusTextInput extends React.Component {
   constructor(props) {
      super(props);
      this.textInput = React.createRef();
   }
   componentDidMount() {      // (2) accessing method of child React component
      this.textInput.current.focusTextInput();
   }
   render() {
      return (<CustomTextInput ref={this.textInput} />);
   }}ReactDOM.render(<AutoFocusTextInput />, document.querySelector('div'));