bravemaster619

Posted on Mar 22, 2020 • Updated on Dec 16, 2020

How to prevent multiple socket connections and events in React

#socket #socketio #react #spa

Multiple socket connections and event bindings can be easily overlooked in SPAs and can cause headaches. I'd like to share my experience of preventing them. In this article, I will use socket.io for Node.js backend and socket.io-client for React frontend.

1. Connect only once

Create a dedicated file for socket connection. For example, create a file in service/socket.js:


import io from "socket.io-client";
import { SOCKET_URL } from "config";

export const socket = io(SOCKET_URL);

You can import this socket instance in other React components whenever necessary:

import {socket} from "service/socket";

function MyComponent() => {
   return(<div></div>)
}

In this way, you can ensure there will be only one socket instance.

2. Bind and emit events only once - put them in the correct place

Consider you're building a React component that connect to a socket server when the page is loaded and show welcome message if the connection is successful. The component will emit an HELLO_THERE event to the server and the server will respond with warm WELCOME_FROM_SERVER event. Where would you place socket event binding and emiting in your React code?

import {socket} from "service/socket";
// NOT HERE (1)
// socket.emit('HELLO_THERE');
function MyComponent() => {

   // NOT HERE EITHER (2)
   // socket.emit('HELLO_THERE');
   const [connected, setConnected] = useState(false);
   // IT IS HERE
   useEffect(() => {
      socket.emit('HELLO_THERE');
      const eventHandler = () => setConnected(true);
      socket.on('WELCOME_FROM_SERVER', eventHandler);
      // unsubscribe from event for preventing memory leaks
      return () => {
         socket.off('WELCOME_FROM_SERVER', eventHandler);
      };
   }, []);
   return (
      <div>
          { connected ? (
               <p>Welcome from server!</p>
          ) : (
               <p>Not connected yet...</p>
          ) }
      </div>
   )
}
export default MyComponent

(1) This will emit the event even if MyComponent is not used.
(2) This will emit the event whenever MyComponent is updated.

* If you're using React classes, componentDidMount will be the right place to use sockets. useEffect(() => {}, []) is almost the same as componentDidMount
** Of course, socket.emit can go anywhere necessary in your code. However, socket.on should be in componentDidMount in most cases.

3. If you're unsure, there is always this hack

If you still cannot figure out why does your component stupidly bind the same listener for multiple times, or if you just want to make sure bind only one listener for one event, you can resort to socket.off.

socket.off('MY_EVENT', doThisOnlyOnce).on('MY_EVENT', doThisOnlyOnce);

UPDATE - useContext approach

If you want to use useContext hook, you can do like this one:

socket.js

import React from "react";
import io from "socket.io-client";
import { SOCKET_URL } from "config";

export const socket = io(SOCKET_URL);
const SocketContext = React.createContext(socket);

Your app.js should look like the following:

import React from "react";
import SocketContext, { socket } from "context/socket";

const App = () => (
   <SocketContext.Provider value={socket}>
      <OtherComponents />
   </SocketContext.Provider>
);

Then anywhere in your component, you can get socket like this:

import React from "react";
import SocketContext from "context/socket";

const OtherComponent = () => {
  const socket = React.useContext(SocketContext);
  ...
};

For more information, you can read my another post here:

How to use socket.io-client correctly in React app

bravemaster619 ・ Dec 16 '20 ・ 3 min read

#socket #react #javascript #webdev

Top comments (12)

Rich Winter • Jun 11 '20

I was working with React and Socket.io and one of the warning messages I got from the React server suggested storing the socket reference in a useRef() hook, but honestly, I kind of like your solution more.

Another additional thought I've seen is to use the .context() API and serve the socket to all components through a Provider.

Bruno Louzada • Oct 9 '20

@bravemaster619 I'm trying to use this strategy with a complex react app, with authentication, tests, I think i solved authentication but the tests are impossible, did you used this with a complex app or just for simple apps? can you help me?

bravemaster619 • Oct 28 '20 • Edited

Sorry for late reply. I see no reason why tests are impossible in this approach. Can you show me some of your code?

Bruno Louzada • Oct 29 '20 • Edited

I implemented socket io as middleware, my problem with socket in component and tests is mocking socket io with jest.mock, I dont want to connect to real server in tests, but with middleware approach I could make tests and it seems better to not depend on component life cycle to handle events;
I had a really hard time configuring websocket with React, with middleware approach I could met all requirements

1 connection per client
Connect based on users only after login
Tests
Update application state
Show snackbars
Change page based on events

Sean_Fang • Feb 3 '22

It is really a great helpful article, many thanks!🙏 I have been recently working with socket io( totally a layman 😂...), and just encountered the issue of multiple listeners attached to a certain event, even I put my socket in my useEffect, the problem still persisted, in the end, it turned out I didnt do cleanup in useEffect. After that, I experimented on it a bit, and found out that those listeners are still there even after the connection is closed, thus next time when a user log back in( in my case), the user wil have multiple listeners fire for a single event. Not quite sure if this is default behavior, but its kinda weird cuz I thought everything will be gone after the connection is closed😅. And one more thing, I personally think that "off() & on()" trick is the safest way to work with socket in react cuz we usually use socket across components, definitely dont wanna trigger the event in multiple places...
Again, thank you for such a great article👍

itminhnhut • Nov 27 '20 • Edited

if i have MyComponent and MyComponent2 use socket.on('receive_event', eventHandler);
if MyComponent2 use socket.off('receive_event').on('receive_event',()=> function)
is MyComponent have is off after on like MyComponent2 ? .
i want MyComponent2 change socket on is MyComponent no action . How ?.