Get ref of child

Example.jsx

class Input extends Component {
  // other stuff
  render() {
    return <input value={this.props.value} onChange={this.props.onChange} />
  }
};

class CoolComponent extends Component {
  // other stuff
  doSomethingWithRealInput() {
    // do something like copy input value to clipboard
    // which requires the input ref
  }
  render() {
    return (
      <div>
        <button onClick={this.doSomethingWithRealInput}>Do something crazy!!</button>
        <Input value={ this.state.value } onChange={ this.update } />
      </div>
    )
  }
}