unclear error message "Provided code is not a loadable module"

[xxyyzz2050]

when I deploy my project to firebase using firebase-tools CLI, I got the following unclear error message

functions[hello(us-central1)]: Deployment error.
Function failed on loading user code. Error message: Provided code is not a loadable module.
Could not load the function, shutting down.

what does this error message mean, and how to fix it?

function
functions/index.js

export const hello= functions.https.onRequest((request, response) => {
  response.send('firebase function works');
});

repo: https://github.com/xxyyzz2050/eldeebCMS
script: npm run start:firebase = npm run build:firebase + npm run serve:firebase

note
firebase serve works fine

edit
I fixed the issue, but please provide us clear error messages

[samtstern]

@xxyyzz2050 can you explain what you did to fix this issue?

[abeisgoat]

Doing a bit of Googling, I can't find any reference to this error anywhere on the internet, which means it's probably from an internal Google service. That's definitely outside my area, but I get the feeling this isn't something easily fixed. If the code isn't a module, we can't really tell you why, we just know it isn't.

[samtstern]

I am pretty sure this error comes from here:
https://github.com/GoogleCloudPlatform/functions-framework-nodejs/blob/2dcb838175c228da2b8ae8f652708a717c6e2f12/src/invoker.ts#L155

But AFAIK the framework is only use in Node 10+ which is why I asked about the node version.

[abeisgoat]

So this isn't an issue for firebase-tools really because if anything, it's a functions-framework bug. Regardless, @xxyyzz2050 says it was user error and since they haven't responded to explain what they did to fix it, i can't really help to improve the error because a module could be invalid for many specific reasons. So I'm gonna close this, but feel free to reopen @xxyyzz2050 if you feel like providing more info.

[ashwingattani]

@xxyyzz2050 can you elaborate on how you fixed the issue?