Differences between socket.io and websockets

Misconceptions

There are few common misconceptions regarding WebSocket and Socket.IO:

The first misconception is that using Socket.IO is significantly easier than using WebSocket which doesn't seem to be the case. See examples below. The second misconception is that WebSocket is not widely supported in the browsers. See below for more info. The third misconception is that Socket.IO downgrades the connection as a fallback on older browsers. It actually assumes that the browser is old and starts an AJAX connection to the server, that gets later upgraded on browsers supporting WebSocket, after some traffic is exchanged. See below for details.

My experiment

I wrote an npm module to demonstrate the difference between WebSocket and Socket.IO:

https://www.npmjs.com/package/websocket-vs-socket.io

https://github.com/rsp/node-websocket-vs-socket.io

It is a simple example of server-side and client-side code - the client connects to the server using either WebSocket or Socket.IO and the server sends three messages in 1s intervals, which are added to the DOM by the client.

Server-side

Compare the server-side example of using WebSocket and Socket.IO to do the same in an Express.js app:

WebSocket Server

WebSocket server example using Express.js:

var path = require('path');
var app = require('express')();
var ws = require('express-ws')(app);
app.get('/', (req, res) => {
  console.error('express connection');
  res.sendFile(path.join(__dirname, 'ws.html'));
});
app.ws('/', (s, req) => {
  console.error('websocket connection');
  for (var t = 0; t < 3; t++)
    setTimeout(() => s.send('message from server', ()=>{}), 1000*t);
});
app.listen(3001, () => console.error('listening on http://localhost:3001/'));
console.error('websocket example');

Source: https://github.com/rsp/node-websocket-vs-socket.io/blob/master/ws.js

Socket.IO Server

Socket.IO server example using Express.js:

var path = require('path');
var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);
app.get('/', (req, res) => {
  console.error('express connection');
  res.sendFile(path.join(__dirname, 'si.html'));
});
io.on('connection', s => {
  console.error('socket.io connection');
  for (var t = 0; t < 3; t++)
    setTimeout(() => s.emit('message', 'message from server'), 1000*t);
});
http.listen(3002, () => console.error('listening on http://localhost:3002/'));
console.error('socket.io example');

Source: https://github.com/rsp/node-websocket-vs-socket.io/blob/master/si.js

Client-side

Compare the client-side example of using WebSocket and Socket.IO to do the same in the browser:

WebSocket Client

WebSocket client example using vanilla JavaScript:

var l = document.getElementById('l');
var log = function (m) {
    var i = document.createElement('li');
    i.innerText = new Date().toISOString()+' '+m;
    l.appendChild(i);
}
log('opening websocket connection');
var s = new WebSocket('ws://'+window.location.host+'/');
s.addEventListener('error', function (m) { log("error"); });
s.addEventListener('open', function (m) { log("websocket connection open"); });
s.addEventListener('message', function (m) { log(m.data); });

Source: https://github.com/rsp/node-websocket-vs-socket.io/blob/master/ws.html

Socket.IO Client

Socket.IO client example using vanilla JavaScript:

var l = document.getElementById('l');
var log = function (m) {
    var i = document.createElement('li');
    i.innerText = new Date().toISOString()+' '+m;
    l.appendChild(i);
}
log('opening socket.io connection');
var s = io();
s.on('connect_error', function (m) { log("error"); });
s.on('connect', function (m) { log("socket.io connection open"); });
s.on('message', function (m) { log(m); });

Source: https://github.com/rsp/node-websocket-vs-socket.io/blob/master/si.html

Network traffic

To see the difference in network traffic you can run my test. Here are the results that I got:

WebSocket Results

2 requests, 1.50 KB, 0.05 s

From those 2 requests:

HTML page itself connection upgrade to WebSocket

(The connection upgrade request is visible on the developer tools with a 101 Switching Protocols response.)

Socket.IO Results

6 requests, 181.56 KB, 0.25 s

From those 6 requests:

the HTML page itself Socket.IO's JavaScript (180 kilobytes) first long polling AJAX request second long polling AJAX request third long polling AJAX request connection upgrade to WebSocket

Screenshots

WebSocket results that I got on localhost:

https://i.stack.imgur.com/e2yY5.png

Socket.IO results that I got on localhost:

https://i.stack.imgur.com/RHymm.png

Test yourself

Quick start:

# Install:
npm i -g websocket-vs-socket.io
# Run the server:
websocket-vs-socket.io

Open http://localhost:3001/ in your browser, open developer tools with Shift+Ctrl+I, open the Network tab and reload the page with Ctrl+R to see the network traffic for the WebSocket version.

Open http://localhost:3002/ in your browser, open developer tools with Shift+Ctrl+I, open the Network tab and reload the page with Ctrl+R to see the network traffic for the Socket.IO version.

To uninstall:

# Uninstall:
npm rm -g websocket-vs-socket.io

Browser compatibility

As of June 2016 WebSocket works on everything except Opera Mini, including IE higher than 9.

This is the browser compatibility of WebSocket on Can I Use as of June 2016:

https://i.stack.imgur.com/igTKM.png

See http://caniuse.com/websockets for up-to-date info.

---

Its advantages are that it simplifies the usage of WebSockets as you described in #2, and probably more importantly it provides fail-overs to other protocols in the event that WebSockets are not supported on the browser or server. I would avoid using WebSockets directly unless you are very familiar with what environments they don't work and you are capable of working around those limitations.

This is a good read on both WebSockets and Socket.IO.

http://davidwalsh.name/websocket

---

tl;dr;

Comparing them is like comparing Restaurant food (maybe expensive sometimes, and maybe not 100% you want it) with homemade food, where you have to gather and grow each one of the ingredients on your own.

Maybe if you just want to eat an apple, the latter is better. But if you want something complicated and you're alone, it's really not worth cooking and making all the ingredients by yourself.

I've worked with both of these. Here is my experience.

SocketIO

Has autoconnect

Has namespaces

Has rooms

Has subscriptions service

Has a pre-designed protocol of communication (talking about the protocol to subscribe, unsubscribe or send a message to a specific room, you must all design them yourself in websockets)

Has good logging support

Has integration with services such as redis

Has fallback in case WS is not supported (well, it's more and more rare circumstance though)

It's a library. Which means, it's actually helping your cause in every way. Websockets is a protocol, not a library, which SocketIO uses anyway.

The whole architecture is supported and designed by someone who is not you, thus you dont have to spend time designing and implementing anything from the above, but you can go straight to coding business rules.

Has a community because it's a library (you can't have a community for HTTP or Websockets :P They're just standards/protocols)

Websockets

You have the absolute control, depending on who you are, this can be very good or very bad

It's as light as it gets (remember, its a protocol, not a library)

You design your own architecture & protocol

Has no autoconnect, you implement it yourself if yo want it

Has no subscription service, you design it

Has no logging, you implement it

Has no fallback support

Has no rooms, or namespaces. If you want such concepts, you implement them yourself

Has no support for anything, you will be the one who implements everything

You first have to focus on the technical parts and designing everything that comes and goes from and to your Websockets

You have to debug your designs first, and this is going to take you a long time

Obviously, you can see I'm biased to SocketIO. I would love to say so, but I'm really really not.

I'm really battling not to use SocketIO. I dont wanna use it. I like designing my own stuff and solving my own problems myself.

But if you want to have a business and not just a 1000 lines project, and you're going to choose Websockets, you're going to have to implement every single thing yourself. You have to debug everything. You have to make your own subscription service. Your own protocol. Your own everything. And you have to make sure everything is quite sophisticated. And you'll make A LOT of mistakes along the way. You'll spend tons of time designing and debugging everything. I did and still do. I'm using websockets and the reason I'm here is because they're unbearable for a one guy trying to deal with solving business rules for his startup and instead dealing with Websocket designing jargon.

Choosing Websockets for a big application ain't an easy option if you're a one guy army or a small team trying to implement complex features. I've wrote more code in Websockets than I ever wrote with SocketIO in the past, for ten times simpler things than I did with SocketIO.

All I have to say is ... Choose SocketIO if you want a finished product and design. (unless you want something very simple in functionality)

---

Im going to provide an argument against using socket.io.

I think using socket.io solely because it has fallbacks isnt a good idea. Let IE8 RIP.

In the past there have been many cases where new versions of NodeJS has broken socket.io. You can check these lists for examples... https://github.com/socketio/socket.io/issues?q=install+error

If you go to develop an Android app or something that needs to work with your existing app, you would probably be okay working with WS right away, socket.io might give you some trouble there...

Plus the WS module for Node.JS is amazingly simple to use.

---

Using Socket.IO is basically like using jQuery - you want to support older browsers, you need to write less code and the library will provide with fallbacks. Socket.io uses the websockets technology if available, and if not, checks the best communication type available and uses it.

---

https://socket.io/docs/#What-Socket-IO-is-not (with my emphasis)

What Socket.IO is not Socket.IO is NOT a WebSocket implementation. Although Socket.IO indeed uses WebSocket as a transport when possible, it adds some metadata to each packet: the packet type, the namespace and the packet id when a message acknowledgement is needed. That is why a WebSocket client will not be able to successfully connect to a Socket.IO server, and a Socket.IO client will not be able to connect to a WebSocket server either. Please see the protocol specification here. // WARNING: the client will NOT be able to connect! const client = io('ws://echo.websocket.org');

---

Even if modern browsers support WebSockets now, I think there is no need to throw SocketIO away and it still has its place in any nowadays project. It's easy to understand, and personally, I learned how WebSockets work thanks to SocketIO.

As said in this topic, there's a plenty of integration libraries for Angular, React, etc. and definition types for TypeScript and other programming languages.

The other point I would add to the differences between Socket.io and WebSockets is that clustering with Socket.io is not a big deal. Socket.io offers Adapters that can be used to link it with Redis to enhance scalability. You have ioredis and socket.io-redis for example.

Yes I know, SocketCluster exists, but that's off-topic.

---

I would like provide one more answer in 2021. socket.io has become actively maintained again since 2020 Sept. During 2019 to 2020 Aug(almost 2 years) there was basically no activity at all and I had thought the project may be dead.

Socket.io also published an article called Why Socket.IO in 2020?, except for a fallback to HTTP long-polling, I think these 2 features are what socket.io provides and websocket lacks of

auto-reconnection

a way to broadcast data to a given set of clients (rooms/namespace)

One more feature I find socket.io convenient is for ws server development, especially I use docker for my server deployment. Because I always start more than 1 server instances, cross ws server communication is a must and socket.io provide https://socket.io/docs/v4/redis-adapter/ for it.

With redis-adapter, scaling server process to multiple nodes is easy while load balance for ws server is hard. Check here https://socket.io/docs/v4/using-multiple-nodes/ for further information.

---

Socket.IO uses WebSocket and when WebSocket is not available uses fallback algo to make real time connections.

---