CODEWITHSUNDEEP
reactjswebsocket
Arpit Sharma
Arpit Sharma

Reputation: 11

React + Socket.io: Duplicate Connection Messages with Different Socket IDs

I'm using Socket.io with React (frontend) and Express (backend). When a user connects, I log "User connected" along with the socket ID. However, I noticed that the message appears twice, each time with a different socket ID. I found that disabling React Strict Mode resolves the issue, but I would like to understand:

  1. Why does this happen in Strict Mode?
  2. How can I fix this without removing Strict Mode?

Upvotes: 1

Views: 21

Answers (1)

bluestar
bluestar

Reputation: 100

Good question! This issue occurs because React Strict Mode in development renders components twice on purpose. This double rendering helps detect potential side effects but can cause unexpected behavior with WebSocket connections like Socket.io.

1.Why Does This Happen in Strict Mode?

React Strict Mode intentionally mounts and unmounts components twice in development. This means that:

  • Your useEffect (or equivalent) runs twice.
  • A new Socket.io connection is created twice.
  • This results in two different socket IDs being logged.

2.How to Fix Without Removing Strict Mode?

If you want to test socket in strict mode, then I think you can use useRef like following:

import { useEffect, useRef } from "react";
import io from "socket.io-client";

const useSocket = () => {
  const socketRef = useRef(null);

  useEffect(() => {
    if (!socketRef.current) {
      socketRef.current = io("http://localhost:5000"); // Backend URL
      console.log("User connected", socketRef.current.id);
    }

    return () => {
      socketRef.current.disconnect();
      socketRef.current = null;
    };
  }, []);

  return socketRef.current;
};

Upvotes: 0

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