react-chat-app/client/src/components/ChatBox/ChatBox.js

import React from 'react';
import { socket } from '../../App'
import Header from './Header/Header'
import './ChatBox.scss'

const ChatBox = ({ user }) => {

  const [messages, setMessages] = React.useState([])
  const chatContentElement = React.useRef(null)
  const inputMessageElement = React.useRef(null)

  const sendMessage = e => {
    e.preventDefault()
    const message = e.target.elements.message

    socket.emit('chat:message', message.value, user.username)
    message.value = ''
  }

  const ChatContent = () => <div ref={chatContentElement} className="chat-content">
    {messages.map((obj, i) => {
      const date = new Date()
      return (
        <div key={i} className='message'>
          <div className="message-username">
            <p>
              {obj.username}
              <span>{`${date.getHours()}:${date.getMinutes()}`}</span>
            </p>
          </div>
          <div className="message-text">
            {obj.message}
          </div>
        </div>
      )
    })}
  </div>

  const ChatInput = () => {
    return (
      <div className="chat-input">
        <form onSubmit={sendMessage}>
          <input ref={inputMessageElement} required type="text" name='message' placeholder='message'/>
          <button>
            <svg width="25" height="23" viewBox="0 0 25 23" fill="none" xmlns="http://www.w3.org/2000/svg">
              <path d="M23.5111 9.27032L3.34053 0.900689C2.49077 0.548052 1.53076 0.703179 0.835207 1.30533C0.139651 1.90757 -0.151267 2.8355 0.0760766 3.72696L1.87144 10.7676H10.6618C11.0663 10.7676 11.3942 11.0955 11.3942 11.5001C11.3942 11.9045 11.0663 12.2325 10.6618 12.2325H1.87144L0.0760766 19.2731C-0.151267 20.1646 0.139602 21.0925 0.835207 21.6947C1.53218 22.2981 2.49229 22.4513 3.34058 22.0994L23.5112 13.7298C24.4295 13.3487 25 12.4943 25 11.5001C25 10.5058 24.4295 9.65132 23.5111 9.27032Z" fill="#0070F3"/>
            </svg>
          </button>
        </form>
      </div>
    )
  }

  React.useEffect(() => {
    socket.on('chat:message', (message, username) => {
      setMessages(messages => ([...messages, { message, username }]))
      chatContentElement.current.scrollTop = chatContentElement.current.scrollHeight
      inputMessageElement.current.focus()
    })
  }, [setMessages]);

  return (
    <div className="chat">
      <Header />
      <ChatContent />
      <ChatInput />
    </div>
  )
}

export default ChatBox