WebSocket vs Socket.IO

Why do we need WebSocket and Socket.IO? Both technologies connect the client and server and provide real-time communication. For example, they are essential for chat apps, multiplayer games, and other scenarios where real-time interaction between the client and server is crucial.

We can achieve "real-time" communication by repeatedly sending HTTP requests at short intervals, but this approach is costly and inefficient for large applications.

WebSocket

WebSocket is an application-layer protocol over TCP that enables bidirectional communication between a client and a server. It establishes a connection through a single HTTP Upgrade request from the client, and the server responds with a status code. If the status code is 101, the connection is established; otherwise, the connection fails. Once established, WebSocket uses a TCP/IP connection to maintain communication.

Socket.IO

Socket.IO is a JavaScript library that uses WebSocket when available to establish a real-time connection. If WebSocket is unavailable, it falls back to long polling. It has the same functionality as WebSocket but includes additional built-in features, making it more advantageous in certain cases.

Which is which?

The actual purpose of both technologies is the same — they enable real-time communication between the client and server. Then which is which?

Connection

Both send periodic heartbeats. The server sends "ping" to the client (or vice versa), and if "pong" is not received, the connection is considered dead. If the connection between the client and server is lost because of a network issue or another reason and no pong arrives for the ping, Socket.IO automatically tries to reconnect. With WebSocket, we must handle reconnections manually.

Fallbacks

WebSocket is a protocol that operates over TCP, while Socket.IO has something called a fallback mechanism, which ensures that Socket.IO uses WebSocket when available and automatically switches to long polling when it is not. Long polling occurs when the client makes a request, and once it receives a response, it immediately sends another request to keep the connection alive.

Broadcasting

It is another built-in feature of Socket.IO. In Socket.IO, we can send messages to as many clients as we want or send them to a specific room. A room is like a group chat. Meanwhile, WebSocket requires manual implementation.

Event-based communication

WebSocket is a raw bidirectional connection that allows message exchange. Meanwhile, in Socket.IO, we can create custom events to handle messages, chat joining/leaving, and more.

Server (Node.js)

const { Server } = require('socket.io')
const io = new Server(3000)

io.on('connection', (socket) => {
  socket.on('custom_event', (data) =>
    socket.emit('response_event', 'Hello from server!'),
  )
})

Client (Browser)

const socket = io('http://localhost:3000')

socket.emit('custom_event', 'Hello from client!')
socket.on('response_event', (data) => console.log(data))

Performance

Because WebSocket is a thin layer over TCP, it has lower latency than Socket.IO, which includes built-in features like event-based communication. When Socket.IO sends a message, it wraps it in additional metadata (e.g., the event name and the data itself).

{ "event": "custom_event", "data": "Hello" }

When to use which?

1. Choose Socket.IO if you want to simplify development with more built-in features and can accept a small overhead (e.g., chat apps, collaborative tools).
2. Choose WebSocket if you want complete freedom over development, are happy to build everything from scratch, and need high performance with low latency (e.g., trading platforms, gaming servers).

My experience

I worked with Socket.IO on my project Temprora. Feel free to check it out and contribute.