Deploy to firebase functions

First, install the Firebase CLI if you don't have it.

npm install -g firebase-tools

Then, run, login to your firebase account and init a project, right after choose option functions and connect it to your project

firebase login
firebase init

Now, you have a folder called functions.

Yes, delete it.

rm -rf functions

Go to the firebase.json file and add the source property to functions, pointing to current directory:

{
  "functions": {
    "source": ".",
    ...
  }

Now install dependencies for firebase

npm install --save firebase-admin
npm install --save firebase-functions
npm install --save-dev firebase-functions-test

and, add the required engine property to your package.json file

  {
    ...
    "engines": {
      "node": "8"
    }
  }

We're almost there. Go to your src/index.js file, remove app.listen(...)

// app.listen(...)

And the last step. Add functions dependency and export the function.

const functions = require('firebase-functions')

// your code here ...

const api = functions.https.onRequest(app)

module.exports = {
  api
}

Now you can deploy your function to firebase

firebase deploy

Ps.: you may have to fix some lint problems before deploy actualy works. Don't give up.

You can always use the firebase.yml configuration (located in .github/workflows folder) to deploy your app to firebase, using github actions.

Thanks and Good luck.