TypeError: ee.on is not a function

[Stankman]

Bug Report

Current Behavior

When running sls offline for a Serverless application using serverless-offline with the configuration below, an error occurs: TypeError: ee.on is not a function. This seems to prevent the expected startup of the local server.

Sample Code

• file: serverless.yml

service: sls-test

provider:
  name: aws
  runtime: nodejs20.x

functions:
  api:
    handler: dist/lambda.handler
    events:
      - http:
          path: /
          method: ANY
      - http:
          path: '{proxy+}'
          method: ANY

package:
  exclude:
    - node_modules/**

plugins:
  - serverless-offline

• file: handler.js

import serverlessExpress from '@codegenie/serverless-express';
import { NestFactory } from "@nestjs/core";
import { AppModule } from "./app.module";
import { Callback, Context, Handler } from 'aws-lambda';

let server : Handler;

export const handler = async (event: any, context: Context, callback: Callback) => {
    if(!server) {
        const app = await NestFactory.create(AppModule);
        await app.init();

        const expressApp = app.getHttpAdapter().getInstance();
        server = serverlessExpress({
            app: expressApp
        });
    }

    return server(event, context, callback);
}

Expected behavior/code

The application should start without errors and expose the API endpoints locally using serverless-offline.

Environment

• serverless version: 4.4.7
• serverless-offline version: 14.3.3
• node.js version: v20.18.0
• OS: macOS 15.0.1

optional, if you are using any of the following frameworks to invoke handlers

• nestJS version: 10.4.5

Possible Solution

It could be helpful to check for compatibility issues with serverless-offline or dependencies like ee-first in conjunction with the current node.js version.

Additional context/Screenshots

Output when running sls offline:

[Error Logs...]
✖ TypeError: ee.on is not a function
...

[lAndresul]

Same issue here

[MehtaManan07]

Same issue happening for me as well, did anyone find a solution??

[DorianMazur]

Hi @Stankman !
Can you post full error with the stacktrace?

[DanielMaranhao]

Hi, I'm facing a similar issue, I believe it is mostly similar to the issue of Stankman. It occurs when trying to access http://localhost:3000/dev. In my case, the stack trace would be the following, but please feel free to post yours if it differs somehow.

TypeError: ee.on is not a function
    at first (C:\Workspaces\ws-nest\serverless-project\node_modules\ee-first\index.js:43:10)
    at onSocket (C:\Workspaces\ws-nest\serverless-project\node_modules\on-finished\index.js:115:16)
    at attachFinishedListener (C:\Workspaces\ws-nest\serverless-project\node_modules\on-finished\index.js:120:5)
    at attachListener (C:\Workspaces\ws-nest\serverless-project\node_modules\on-finished\index.js:147:5)
    at onFinished (C:\Workspaces\ws-nest\serverless-project\node_modules\on-finished\index.js:53:3)
    at send (C:\Workspaces\ws-nest\serverless-project\node_modules\finalhandler\index.js:319:3)
    at C:\Workspaces\ws-nest\serverless-project\node_modules\finalhandler\index.js:135:5
    at C:\Workspaces\ws-nest\serverless-project\node_modules\express\lib\router\index.js:646:15
    at next (C:\Workspaces\ws-nest\serverless-project\node_modules\express\lib\router\index.js:216:14)
    at Function.handle (C:\Workspaces\ws-nest\serverless-project\node_modules\express\lib\router\index.js:175:3)

[scryan7371]

Same Issue here.

✖ TypeError: ee.on is not a function
at first (/Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/ee-first/index.js:43:10)
at onSocket (/Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/on-finished/index.js:115:16)
at attachFinishedListener (/Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/on-finished/index.js:120:5)
at attachListener (/Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/on-finished/index.js:147:5)
at onFinished (/Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/on-finished/index.js:53:3)
at send (/Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/finalhandler/index.js:319:3)
at /Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/finalhandler/index.js:135:5
at /Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/express/lib/router/index.js:646:15
at next (/Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/express/lib/router/index.js:216:14)
at Function.handle (/Users/scottryan/GIT_WORKING/joinourplans/joinourplans-server/node_modules/express/lib/router/index.js:175:3)

[Mujtaba52]

yup same issue here :/

[Mujtaba52]

Guys I encountered the same issue. It seems the Lambda function doesn't work for the base route (/). To troubleshoot, try clearing the cache and create a test route, like /hello, then access it via http://localhost:3000/dev/hello. This worked for me, while accessing http://localhost:3000/dev still fails. I'm not certain of the exact cause, but this workaround might help!

[leandromatos]

The way that I found to handle this problem was to parse the path before returning the server instance:

if (event.path === '' || event.path === undefined) event.path = '/';

The entire code:

import { NestFactory } from '@nestjs/core';
import serverlessExpress from '@vendia/serverless-express';
import { Callback, Context, Handler } from 'aws-lambda';
import { ReplaySubject, firstValueFrom } from 'rxjs';
import { FooModule } from './foo.module';

// Declare a ReplaySubject to store the serverlessExpress instance.
const serverSubject = new ReplaySubject<Handler>();

async function bootstrap(): Promise<Handler> {
  console.log('COLD START: Initializing Nest');

  const app = await NestFactory.create(FooModule);

  await app.init();

  const expressApp = app.getHttpAdapter().getInstance();
  return serverlessExpress({ app: expressApp });
}

// Do not wait for lambdaHandler to be called before bootstraping Nest.
// Pass the result of bootstrap() into the ReplaySubject
bootstrap().then((server) => serverSubject.next(server));

type EventPayload = {
  [key: string]: any;
};

export const handler: Handler = async (
  event: EventPayload,
  context: Context,
  callback: Callback,
) => {
  // Handle edge cases for root path
  if (event.path === '' || event.path === undefined) event.path = '/';

  // Convert the ReplaySubject to a Promise.
  // Wait for bootstrap to finish, then start handling requests.
  const server = await firstValueFrom(serverSubject);
  return server(event, context, callback);
};