Example of ReactJS Ref and React.createRef()

import React, { Component } from 'react'

export class Contact extends Component {
    constructor(props){
       super(props);
       this.state={name:"Jahid",message:""};
       this.txtNameRef=React.createRef();
    }

    componentDidMount(){
      this.txtNameRef.current.focus();

    }

    messageHandler=()=>{
      this.setState({message:"Thank you"});
    }

    nameHandler=(event)=>{
        this.setState({name:event.target.value});//this.txtNameRef.current.value

    }
    render() {
        return (
            <div>
                Hello {this.state.name} {this.state.message}
                <input type="text" onChange={this.nameHandler} ref={this.txtNameRef} />
                <button onClick={this.messageHandler}>Message</button>
            </div>
        )
    }
}

export default Contact