Nodejs event emitter implementation in Nextjs 13 or 14

[torver213]

How do i make nodejs event emitter object to listen to emitted events globally within my nextjs13 application just like in normal nodejs environment?

I have a file post.js where a user creates a new post. I want to promptly return the response back to the user, emit an event where a handler function will listen to the emitted event in another file & perform some other tasks in the background like updating post tags count and then finally emitting an sse(server sent event) to client app to notify other connected clients.

First of all, i created a file known as eventEmitter.js where I created a single instance to be used within my application below;

    //eventEmitter.js

    import { EventEmitter } from 'node:events';

    const eventEmitter = new EventEmitter({captureRejections: true})

    export default eventEmitter;

    //post.js
  
    import eventEmitter from './eventEmitter'
  
    const insertPost = async() => {
       // perform db post insert
       
       //emit an event to be listened to perform a background task
       eventEmitter.emit("PING", "hello world");
       
       //return 
       return {id: 1, title: 'hello' }
   }
   

   insertPost()
   
   
    // this only works when the listener is in the same file with the emitted event
   eventEmitter.on("PING", (ev) => {
        console.log(ev)
   });
   

    //listener.js
  
    import eventEmitter from './eventEmitter'
    // this doesn't work i.e the event is not captured in the file
   eventEmitter.on("PING", (ev) => {
        console.log(ev)
   });

 //route.js
  export function GET(request: Request) {
       const responseStream = new TransformStream();
       const writer = responseStream.writable.getWriter();
       const encoder = new TextEncoder();
       //... other code
      
       // this doesn't work i.e the event is not captured in the file
      eventEmitter.on("PING", (ev) => {
        console.log(ev)
     });
     
     // my streaming logic
}

My question is, how do i listen to the emitted event in other files like listener.js and route.js files other than just post.js file?

I want to listen to the emitted events globally within my nextjs app

The above works seamlessly in a nodejs environment and i expected it to work in nextjs environment too.

PS: I'm using nextjs App Router

Please help.

[jonshipman]

I mean, couldn't you have a src/lib/application.ts and listen from there?

import { EventEmitter } from 'node:events';

class ApplicationEmitter extends EventEmitter {}

export const app = new ApplicationEmitter();

app.on('something', function() {
	// do something...
});

The issue you're running into is that on that GET request, it only fires during the polling. Not knowing where the app is hosted is another issue as "serverless" hosts spin up instances on request. If you are on a traditional server then you can just import '@/lib/application' into 'src/middleware.ts' and it should work with emits.

Also, it's never a good idea to wrap listeners in functions. That's a quick way to a memory leak my friend. Instead emit a callback. e.g. eventEmitter.emit('PING', function callback() { /* awesome */ }); then in the application.ts, eventEmitter.on('PING', function(cb) { cb(); });

[latifs]

Hi @techfortified,
have you been able to solve that?
thanks