jszmq

jszmq is a port of zeromq to JavaScript, focused on browser runtimes via the WebSocket transport (ZWS 2.0).

The API mirrors zeromq.js.

Requirements

• Browser-first: consumed through a bundler (Vite, webpack, esbuild, tsx, etc.). The package ships ESM only with extensionless internal imports.
• Node ≥22 if used server-side (relies on the global WebSocket).

Compatibility with ZeroMQ

The WebSocket transport is supported by zeromq when compiled from source.

Other ports of zeromq (NetMQ for C#, JeroMQ for Java) don't yet support the WebSocket transport.

Compatibility with ZWS 1.0, zwssock, JSMQ and NetMQ.WebSockets

Not compatible with ZWS 1.0.

Installation

pnpm add @blueyerobotics/jszmq

Supported socket types

• Pub
• Sub
• XPub
• XSub
• Dealer
• Router
• Req
• Rep
• Push
• Pull
• Pair

How to use

import * as zmq from '@blueyerobotics/jszmq'

Creating a socket

Either via the socket type class:

const dealer = new zmq.Dealer()

or via the socket factory (matches zeromq.js):

const dealer = zmq.socket('dealer')

Bind

bind is Node-only (it starts a WebSocket server). Browsers can only connect.

import { Router } from '@blueyerobotics/jszmq'

const router = new Router()
router.bind('ws://localhost:80')

You can also share an existing HTTP server across multiple sockets:

import { createServer } from 'http'
import { Rep, Pub } from '@blueyerobotics/jszmq'

const server = createServer()

const rep = new Rep()
const pub = new Pub()

rep.bind('ws://localhost:80/reqrep', server)
pub.bind('ws://localhost:80/pubsub', server)

server.listen(80)

bindSync is an alias for bind, kept for zeromq.js compatibility.

Sending

send accepts a single frame or an array of frames. Each frame is either a string (encoded as UTF-8) or a Uint8Array.

socket.send('Hello')                                      // single frame
socket.send(['Hello', 'World'])                           // multiple frames
socket.send([new TextEncoder().encode('Hello')])          // raw bytes

Receiving

Sockets emit a message event. Each frame is passed as a separate argument to the listener; every frame is a Uint8Array.

const decode = (b) => new TextDecoder().decode(b)

socket.on('message', msg => console.log(decode(msg)))                              // one frame
socket.on('message', (a, b) => console.log(decode(a), decode(b)))                  // two frames
socket.on('message', (...frames) => frames.forEach(f => console.log(decode(f))))   // any number

Examples

Push/Pull

A producer pushes work onto a socket and a worker pulls it.

producer.js

import { Push } from '@blueyerobotics/jszmq'

const sock = new Push()
sock.bind('ws://127.0.0.1:3000')
console.log('Producer bound to port 3000')

setInterval(() => {
  console.log('sending work')
  sock.send('some work')
}, 500)

worker.js

import { Pull } from '@blueyerobotics/jszmq'

const decode = (b) => new TextDecoder().decode(b)
const sock = new Pull()
sock.connect('ws://127.0.0.1:3000')
console.log('Worker connected to port 3000')

sock.on('message', msg => {
  console.log('work:', decode(msg))
})

Pub/Sub

Publisher: pubber.js

import { Pub } from '@blueyerobotics/jszmq'

const sock = new Pub()
sock.bind('ws://127.0.0.1:3000')
console.log('Publisher bound to port 3000')

setInterval(() => {
  console.log('sending a multipart message envelope')
  sock.send(['kitty cats', 'meow!'])
}, 500)

Subscriber: subber.js

import { Sub } from '@blueyerobotics/jszmq'

const decode = (b) => new TextDecoder().decode(b)
const sock = new Sub()
sock.connect('ws://127.0.0.1:3000')
sock.subscribe('kitty cats')
console.log('Subscriber connected to port 3000')

sock.on('message', (topic, message) => {
  console.log('topic:', decode(topic), 'message:', decode(message))
})