Getting Started with js-libp2p

This is the first in a series of tutorials on working with libp2p’s javascript implementation, js-libp2p.

We’ll cover setting up an empty project, creating a libp2p “bundle” with some basic functionality, and finally we’ll send ping messages back and forth between two peers.

Install node.js

Working with js-libp2p requires node.js for development. If you haven’t already, install node using whatever package manager you prefer or using the official installer.

We recommend using the latest stable version of node, but anything fairly recent should work fine. If you want to see how low you can go, the current version requirements can always be found at the js-libp2p project page.

Create an empty project

We need a place to put our work, so open a terminal to make a new directory for your project somewhere and set it up as an npm project:

# create a directory for the project and `cd` into it
> mkdir hello-libp2p
> mkdir hello-libp2p/src
> cd hello-libp2p

# make it a git repository
> git init .

# make it an npm project. fill in the prompts with info for your project
# when asked for your project's entry point, enter "src/index.js"
> npm init

Side note: throughout this tutorial, we use the > character to indicate your terminal’s shell prompt. When following along, don’t type the > character, or you’ll get some weird errors.

Build a libp2p bundle

libp2p is a very modular framework, which allows javascript devs to target different runtime environments and opt-in to various features by including a custom selection of modules.

Because every application is different, we recommend building a “bundle” with just the modules you need. You can even make more than one, if you want to target multiple javascript runtimes with different features. For example, the IPFS project uses two libp2p bundles, one for node.js and one for the browser.

Since, we’re here to learn how libp2p works, we’re going to start from scratch and define our own bundle. We’ll start with a very simple bundle and add features as we need them.

First, install the libp2p dependency. We’ll also need at least one transport module, so we’ll pull in libp2p-tcp as well, and the @nodeutils/defaults-deep helper which we’ll use when building the bundle.

npm install --save libp2p libp2p-tcp @nodeutils/defaults-deep

In a production application, it may make sense to create a separate npm module for your bundle, which will give you one place to manage the libp2p dependencies for all your javascript projects. In that case, you should not depend on libp2p directly in your application. Instead you’d depend on your bundle, which would in turn depend on libp2p and whatever modules (transports, etc) you might need.

For this tutorial, our bundle will just be a javascript file in our application source.

Make a directory called src/p2p and a file called src/p2p/index.js with the following content:

const Libp2p = require('libp2p')
const TCP = require('libp2p-tcp')

const defaultsDeep = require('@nodeutils/defaults-deep')

const DEFAULT_OPTS = {
  modules: {
    transport: [

class P2PNode extends Libp2p {
  constructor (opts) {
    super(defaultsDeep(opts, DEFAULT_OPTS))

The libp2p module exports a libp2p.Node class which we extend into our own P2PNode class.

Right now our class just adds the libp2p-tcp transport module to the default constructor options of the base class. As we go, we’ll extend our bundle to include more transports and configure other aspects of the libp2p stack.

Create an instance of a libp2p node

Using the bundle we defined above, we can create a new P2PNode instance.

To do so, create a file called src/index.js and make it look like this:

const multiaddr = require('multiaddr')
const PeerInfo = require('peer-info')
const {P2PNode} = require('./p2p')

function createPeer(callback) {
  // create a new PeerInfo object with a newly-generated PeerId
  PeerInfo.create((err, peerInfo) => {
    if (err) {
      return callback(err)

    // add a listen address to accept TCP connections on a random port
    const listenAddress = multiaddr(`/ip4/`)

    const peer = new P2PNode({peerInfo})
    // register an event handler for errors.
    // here we're just going to print and re-throw the error
    // to kill the program
    peer.on('error', err => {
      console.error('libp2p error: ', err)
      throw err

    callback(null, peer)

We start out by importing a few modules. Apart from the P2PNode bundle we defined earlier, we have multiaddr, the javascript multiaddress library, and peer-info, which contains a PeerId and a set of multiaddresses that are associated with a peer.

The constructor for our bundle requires a peerInfo argument. This can either be generated on-the-fly or loaded from a byte buffer or JSON object. In our createPeer function, we’re generating a new PeerInfo object for our peer using PeerInfo.create. This will generate a new PeerId containing a newly-generated cryptographic key pair.

Because generating the key pair requires some computation, PeerInfo.create is an asynchronous operation. libp2p uses node-style callbacks for most asynchronous operations, and real-world code and more complex examples will often use helpers like async/waterfall to compose chains of async operations. Since this is a fairly simple example, we’re just going to use the callbacks as-is and chain them together the “old fashioned way”.

Once we have our PeerInfo, we next create a multiaddress for /ip4/, which is the localhost IPv4 address on the special TCP port 0. Using port 0 tells the operating system to randomly assign us an open port.

Adding the new multiaddr to our PeerInfo object will cause our node to try to listen on that address when the node starts.

Next we create our peer, passing in the peerInfo constructor option, and we register a simple error handler to catch errors that might occur during the lifetime of our peer.

Start the node and listen for connections

Now we can call the createPeer function above and start listening for connections.

Just below the createPeer function definition, add some code to start the peer and print our listening address:

function handleStart(peer) {
      // get the list of addresses for our peer now that it's started.
      // there should be one address of the form
      // `/ip4/${assignedPort}/ipfs/${generatedPeerId}`,
      // where `assignedPort` is randomly chosen by the operating system
      // and `generatedPeerId` is generated in the `createPeer` function above.
      const addresses = peer.peerInfo.multiaddrs.toArray()
      console.log('peer started. listening on addresses:')
      addresses.forEach(addr => console.log(addr.toString()))

// main entry point
createPeer((err, peer) => {
  if (err) {
    throw err

  peer.start(err => {
    if (err) {
      throw err


Try running the code with node src/index.js. You should see something like:

peer started. listening on addresses:

Each time you run the program, you should see a different tcp port number and PeerId hash (the QmPfH3qx5fyfUgxacrZ1WNC1GwXmY5kWzns3Fc9KAwZRgJ string above).

Add multiplexing and encryption

We can now start a node and listen for connections, but we can’t really do anything yet. This is because we’re missing a key libp2p component called a stream multiplexer, which lets us interleave multiple independent streams of communication across one network connection.

While we’re at it, we’ll also add support for encrypted communication, which is something most real-world applications will need to support.

Lets add two new dependencies:

npm install --save libp2p-mplex libp2p-secio

And we’ll need to edit our bundle. Open src/p2p/index.js and import the new modules:

const Multiplex = require('libp2p-mplex')
const SECIO = require('libp2p-secio')

Then change the DEFAULT_OPTS constant to look like this:

const DEFAULT_OPTS = {
  modules: {
    transport: [
    connEncryption: [
    streamMuxer: [

Thats it! Now we can open multiple independent streams over our single TCP connection, and our connection will be upgraded to a securely encrypted channel using the secio module.

Lets play ping pong!

Now that we have the basic building blocks of transport, multiplexing, and security in place, we can start communicating!

The base libp2p.Node class that we based our bundle on registers one built-in protocol handler for us, the ping protocol. That means that other peers can dial us and send us ping messages, and we’ll send back a “pong” so they know we’re alive and can measure the latency between us.

While we respond to pings automatically, we need to do a bit of wiring to send them.

Let’s add a ping method to our P2PNode class so we can send pings to other peers.

Change the definition of P2PNode in src/p2p/index.js to this:

const Ping = require('libp2p-ping')

class P2PNode extends Libp2p {
  constructor (opts) {
    super(defaultsDeep(opts, DEFAULT_OPTS))

  ping (remotePeerInfo, callback) {
    const p = new Ping(this._switch, remotePeerInfo)
    p.on('ping', time => {
      p.stop() // stop sending pings
      callback(null, time)
    p.on('error', callback)

Now we can accept have our program accept the multiaddress of another peer as a command line argument and try to ping it.

To do so, we’ll need to add a couple things to src/index.js. First, require the process module so we can get the command line arguments:

const process = require('process')

Then we’ll add a function to parse a multiaddress from the command line and try to ping the remote peer:

const PeerId = require('peer-id')

function pingRemotePeer(localPeer) {
  if (process.argv.length < 3) {
    return console.log('no remote peer address given, skipping ping')
  const remoteAddr = multiaddr(process.argv[2])

  // Convert the multiaddress into a PeerInfo object
  const peerId = PeerId.createFromB58String(remoteAddr.getPeerId())
  const remotePeerInfo = new PeerInfo(peerId)

  console.log('pinging remote peer at ', remoteAddr.toString()), (err, time) => {
    if (err) {
      return console.error('error pinging: ', err)
    console.log(`pinged ${remoteAddr.toString()} in ${time}ms`)

And finally, in our handleStart function, just after we log our listen address, add this line:


Now we can start one instance with no arguments:

> node src/index.js
peer started. listening on addresses:
no remote peer address given, skipping ping

Grab the /ip4/... address printed above and use it as an argument to another instance. In a new terminal:

> node src/index.js /ip4/
peer started. listening on addresses:
pinging remote peer at  /ip4/
pinged /ip4/ in 6ms

Success! Our two peers are now communicating over a multiplexed, secure channel. Sure, they can only say “ping”, but it’s a start!