Full socket.io client and server example

_Full-socketio-client-and-server-example.md

Full socket.io client and server example

Last updated: 2021-02-21, tested with socket.io v3.1.1

This is the simplest implementation you will find for a client/server WebSockets architecture using socket.io.

To see a full explanation, read my answer on SO here: https://stackoverflow.com/a/24232050/778272.

If you're looking for examples using frameworks, check these links:

• socket.io + Express
• socket.io + Restify

How to run

Create a folder, run npm init -f on it and paste both server.js and client.js there (see files below). Needless to say, you must have Node.js installed on your system.

Install the required libraries:

npm install [email protected]
npm install [email protected]

Run the server:

node server

Open other terminal windows and spawn as many clients as you want by running:

node client

client.js

const
    io = require("socket.io-client"),
    ioClient = io.connect("http://localhost:8000");

ioClient.on("seq-num", (msg) => console.info(msg));

server.js

const
    {Server} = require("socket.io"),
    server = new Server(8000);

let
    sequenceNumberByClient = new Map();

// event fired every time a new client connects:
server.on("connection", (socket) => {
    console.info(`Client connected [id=${socket.id}]`);
    // initialize this client's sequence number
    sequenceNumberByClient.set(socket, 1);

    // when socket disconnects, remove it from the list:
    socket.on("disconnect", () => {
        sequenceNumberByClient.delete(socket);
        console.info(`Client gone [id=${socket.id}]`);
    });
});

// sends each client its current sequence number
setInterval(() => {
    for (const [client, sequenceNumber] of sequenceNumberByClient.entries()) {
        client.emit("seq-num", sequenceNumber);
        sequenceNumberByClient.set(client, sequenceNumber + 1);
    }
}, 1000);

Thanks for the gist.
You can also use room concept of socket.io, instead of a global variables, to store users.

If one is only keeping track of users, using rooms seems like a nice suggestion indeed.

In the example above, however, I also keep a state for each user (their current sequence number). I did this to illustrate how one would store data for each user.

Regarding your mention of the use of global variables: in my example, the Map variable is only visible within the module. It could also be easily turned into an instance member by encapsulating the login within a class (which I would probably do if the logic got more involved).

I would like to mention that the room is also useful when you have one user connected from multiple devices, in your example, you have to do more tweaks in this situation. Moreover, the room will delete users as soon as they disconnect, so you don't have to track their status.

Exactly what I needed, you're the man