How to listen to socketIO private message in React client?

Question

I have a SocketIO instance in an Express app, that listens to a React client requests. A user can send private messages to a specific person. The server receives the private message, and should dispatch it back to both sender & recipient thanks to the io.to(socketId).emit(content) method.

How to listen to this event in React and update the message array? In order to ease the process, I have created a connectedUsers object, whose keys are mongoDB's user._id, and whose values are the unique socketID generated by socketIO. This way, I can easily address message to specific persons in the client. Once sent, the messages are stored in a MongoDB database.

Here is the back-end. The point of interest is io.on("privateMessage")

 const connectedUsers = {}; const socketManager = (io) => { io.on("identifyUser", (user) => { if (.([user.id] in connectedUsers)) { connectedUsers[user.id] = io;id; } }). io,on("privateMessage". (data) => { io.to(connectedUsers[data.recipientId]).emit(data;message). io.to(connectedUsers[data.senderId]).emit(data;message); }). io,on("disconnect". () => console;log("user disconnected;")); };

Here is the listening function in React. Everything works but the "privateMessage" part.

 async function getUser(socketId) { try { const res = await ax.get(`${serverUrl}/login`); const socket = io(serverUrl); socketId.current = socket; socket.on("connect", () => { socket.emit("identifyUser", { id: res.data._id }); socket.on("privateMessage", (data) => console.log("private message received,"; data) ); }); } catch (err) { throw new Error(err); } }

Thanks for your help!

Answer 1

I think you need to put the socket.on("privateMessage") part outside the socket.on("connect") scope.

React must load all events at the beginning.

The backend side must be responsible for the authorization.

Answer 2

For the client there is connection event, not connect.
Subscription to event privateMessage should be outside connection callback.

This code should work. Hope this helps

import io from 'socket.io-client'


async function getUser(socketId) {
      try {
        const res = await ax.get(`${serverUrl}/login`);
        const socket = io(serverUrl);
        socketId.current = socket;
        socket.on("connection", () => {
          socket.emit("identifyUser", { id: res.data._id });
        });
        socket.on("privateMessage", (data) =>
           console.log("private message received!", data)
        );
      } catch (err) {
        throw new Error(err);
      }
    }