call-child-method-from-parent.jsx

class Child extends React.Component {
  greeting() {
    return 'hello world';
  }
}
class Parent extends React.Component {
  render() {
    return (
      <TheChild ref='foo' />
    )
  }
  componentDidMount() {
    const bar = this.refs.foo.greeting();
    // bar is now 'hello world'
  }
}