ref-class-component.js

import React, { Component, createRef } from "react";

class CustomTextInput extends Component {
  textInput = createRef();

  focusTextInput = () => this.textInput.current.focus();

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