//App.js

import Button from Button.js

class App {
    ref = React.createRef();

    componenentDidMount() {
        this.button.focus();
    }

    render() {
        return (<InputText ref={this.button}/>);
    }
}

//InputText.js
export default class InputText {
    render() {
        return (<input type="text"/>);
    }
}