What is an example of the simplest possible Socket.io example?


So, I have been trying to understand Socket.io lately, but I am not a supergreat programmer, and almost every example I can find on the web (believe me I have looked for hours and hours), has extra stuff that complicates things. A lot of the examples do a bunch of things that confuse me, or connect to some weird database, or use coffeescript or tons of JS libraries that clutter things up.

I'd love to see a basic, functioning example where the server just sends a message to the client every 10 seconds, saying what time it is, and the client writes that data to the page or throws up an alert, something very simple. Then I can figure things out from there, add stuff I need like db connections, etc. And yes I have checked the examples on the socket.io site and they don't work for me, and I don't understand what they do.

3/28/2012 8:03:53 PM

Accepted Answer

Edit: I feel it's better for anyone to consult the excellent chat example on the Socket.IO getting started page. The API has been quite simplified since I provided this answer. That being said, here is the original answer updated small-small for the newer API.

Just because I feel nice today:


<!doctype html>
        <script src='/socket.io/socket.io.js'></script>
            var socket = io();

            socket.on('welcome', function(data) {

                // Respond with a message including this clients' id sent from the server
                socket.emit('i am client', {data: 'foo!', id: data.id});
            socket.on('time', function(data) {
            socket.on('error', console.error.bind(console));
            socket.on('message', console.log.bind(console));

            function addMessage(message) {
                var text = document.createTextNode(message),
                    el = document.createElement('li'),
                    messages = document.getElementById('messages');

        <ul id='messages'></ul>


var http = require('http'),
    fs = require('fs'),
    // NEVER use a Sync function except at start-up!
    index = fs.readFileSync(__dirname + '/index.html');

// Send index.html to all requests
var app = http.createServer(function(req, res) {
    res.writeHead(200, {'Content-Type': 'text/html'});

// Socket.io server listens to our app
var io = require('socket.io').listen(app);

// Send current time to all connected clients
function sendTime() {
    io.emit('time', { time: new Date().toJSON() });

// Send current time every 10 secs
setInterval(sendTime, 10000);

// Emit welcome message on connection
io.on('connection', function(socket) {
    // Use socket to communicate with this particular client only, sending it it's own id
    socket.emit('welcome', { message: 'Welcome!', id: socket.id });

    socket.on('i am client', console.log);

5/1/2015 7:03:02 AM

Here is my submission!

if you put this code into a file called hello.js and run it using node hello.js it should print out the message hello, it has been sent through 2 sockets.

The code shows how to handle the variables for a hello message bounced from the client to the server via the section of code labelled //Mirror.

The variable names are declared locally rather than all at the top because they are only used in each of the sections between the comments. Each of these could be in a separate file and run as its own node.

// Server
var io1 = require('socket.io').listen(8321);

io1.on('connection', function(socket1) {
  socket1.on('bar', function(msg1) {

// Mirror
var ioIn = require('socket.io').listen(8123);
var ioOut = require('socket.io-client');
var socketOut = ioOut.connect('http://localhost:8321');

ioIn.on('connection', function(socketIn) {
  socketIn.on('foo', function(msg) {
    socketOut.emit('bar', msg);

// Client
var io2 = require('socket.io-client');
var socket2 = io2.connect('http://localhost:8123');

var msg2 = "hello";
socket2.emit('foo', msg2);

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