Listen to a channel from any back end file?

[respectabiggle]

Hello.

I'm hoping to emit from one back end file, and listen to the channel at a different back end file. No front end at all.

Emitting file "emit.js"

import { createServer } from 'http'
const httpServer = createServer()
httpServer.listen(3000)
import { Server } from 'socket.io'
const io = new Server(httpServer)

import { WebSocket } from 'ws'
const ws = new WebSocket('wss://ws.coincap.io/prices?assets=ethereum')

export const emit = async function (){

ws.on('message', (event) => {

let data = JSON.parse(event)
console.log(data)

io.emit('test', data)

})

}

Listening file "listen.js"

export const listen = async function (){

// await io.on('test', (event) => {

// let data = JSON.parse(event)
// console.log(data)

// })

}

What is the simple way to set this up? Thank you so much!!!!

[darrachequesne]

Are those two files run in the same Node.js process? In that case, you could use a simple EventEmitter:

emit.js

import { WebSocket } from 'ws'
import { EventEmitter } from 'node:events';

const ws = new WebSocket('wss://ws.coincap.io/prices?assets=ethereum')

export const myEventBus = new EventEmitter();

ws.on('message', (event) => {
  let data = JSON.parse(event)

  myEventBus.emit('test', data)
})

listen.js

import { myEventBus } from './emit';

myEventBus.on('test', (data) => {
  // ...
});

Reference: https://nodejs.org/api/events.html

If you have two distinct Node.js processes, then you can indeed create a Socket.IO connection:

import { io } from 'socket.io-client'

export const listen = async function (){

  const socket = io('http://localhost:3000');
  
  socket.on('test', (data) => {
    // ...
  })
}

[respectabiggle]

Thank you for telling me about EventEmitter !
It works and is awesome.

For two distinct Node processes, should I start with https://nodejs.org/api/cluster.html ?

Also, should I understand from your answer that there is not a native function in Socket.io
to broadcast to the rest of the back end,
within one single Node process?

Thank you again for being friendly!