how react programmatically focus input

The way you have used refs is not the most preferred way or else its not the best practice anymore . try some thing like this

class MyClass extends React.Component {
  constructor(props) {
    super(props);
    this.focus = this.focus.bind(this);
  }

  focus() {
    this.textInput.current.focus();
  }

  render() {

    return (
      <div>
        <input
          type="text"
          ref={(input) => { this.textInput = input; }} />
        <input
          type="button"
          value="Set Focus"
          onClick={this.focus}
        />
      </div>
    );
  }
}

Update
From React 16.3 upwards you can use the React.createRef() API

class MyClass extends React.Component {
  constructor(props) {
    super(props);
    // create a ref to store the textInput DOM element
    this.textInput = React.createRef();
    this.focus = this.focus.bind(this);
  }

  focus() {
    // Explicitly focus the text input using the raw DOM API
    // Note: we're accessing "current" to get the DOM node
    this.textInput.current.focus();
  }

  render() {
    // tell React that we want to associate the <input> ref
    // with the `textInput` that we created in the constructor
    return (
      <div>
        <input
          type="text"
          ref={this.textInput} />
        <input
          type="button"
          value="Set Focus"
          onClick={this.focus}
        />
      </div>
    );
  }
}

From React 18.xx upwards you can use the useRef Hook

import React, { useRef } from "react";

export const Form = () => {
  const inputRef = useRef(null);

  const focus = () => {
    inputRef.current.focus();
  };

  return (
    <div>
      <input type="text" ref={inputRef} />
      <input type="button" value="Set Focus" onClick={focus} />
    </div>
  );
};