Focusing.js

import React from 'react';
import ReactDOM from 'react-dom';

class MyComponent extends React.Component {
  constructor(props){
    super(props);
    this.focus = this.focus.bind(this);
  }

  focus() {
    // explicitly focus the text input using the raw DOM API
    this.textInput.focus();
  }

  render() {
    return (
      <div>
        <input type="text" ref={input => this.textInput = input} />
        <input type="button" value={"Focus the text"} onClick={this.focus} />
      </div>
    );
  }
}

ReactDOM.render(
  <MyComponent />,
  document.getElementById('root')
);