ref.js

class SomeComponent {
	sayHello() {
		console.log("Hello")
	}
	render() {
		return <div>123</div>
	}
}

class SomeParentComponent {
	render() {
		return (
			<div>
				<SomeComponent ref={instance => this._instance = instance} />
			</div>
		);
	}

	componentDidMount() {
		// :(
		this._instance.sayHello();
	}
}