Firebase - Cloud Functions in CoffeeScript - firebase

Question

I've read somewhere that you can write your Cloud Functions using CoffeeScript, but I'm not sure how.
I did
npm install --save-dev coffeescript
npm install --save-dev coffee-loader
in the functions directory and the devDependencies object does show the libs in package.json
"devDependencies": {
"coffee-loader": "^0.9.0",
"coffeescript": "^2.4.1",
"firebase-functions-test": "^0.1.6"
},
but doing
const backend = require('backend.coffee')
in index.js results in
Cannot find module 'backend.coffee'
Edit: The above error is solved by using a relative path (./backend.coffee), thanks #caffeinated.tech, but now the coffee file is being interpreted as simple JS code and fails.
The contents of package.json:
{
"name": "functions",
"description": "Cloud Functions for Firebase",
"scripts": {
"serve": "firebase serve --only functions",
"shell": "firebase functions:shell",
"start": "npm run shell",
"deploy": "firebase deploy --only functions",
"logs": "firebase functions:log"
},
"engines": {
"node": "8"
},
"dependencies": {
"firebase-admin": "^8.0.0",
"firebase-functions": "^3.1.0",
"nodemailer": "^6.3.1",
"qrcode": "^1.4.2"
},
"devDependencies": {
"coffee-loader": "^0.9.0",
"coffeescript": "^2.4.1",
"eslint": "^6.5.1",
"firebase-functions-test": "^0.1.6"
},
"private": true
}