firebase serve is not compiling typescript code before start

Question

I've a very simple typescript firebase function project... the code works and is very simple, but there is something in the project configuration wrong that makes firebase serve NOT recompile the code before starting the server. at same time firebase deploy works perfectly

the project sits as

firebase
-.firebaserc
-firebase.json
-functions
--package.json
--tsconfig.json
--src
---...all the code goes here
--built
---...code after compiled goes here

this is the content of firebase.json

{
  "functions": [
    {
      "source": "functions",
      "codebase": "default",
      "ignore": [
        "node_modules",
        ".git",
        "firebase-debug.log",
        "firebase-debug.*.log"
      ],
      "predeploy": "npm --prefix functions run build" 
    }
  ]
}

and this is the content of package.json

{
  "name": "functions",
  "scripts": {
    "build": "tsc",
    "build:watch": "tsc --watch",
    "clean-build": "for /D %i in (built\\*) do @rd /s /q \"%i\" & del /q built\\*.*",
    "serve": "npm run clean-build && npm run build && firebase emulators:start --only functions",
    "shell": "npm run clean-build && npm run build && firebase functions:shell",
    "start": "npm run clean-build && npm run shell",
    "deploy": "firebase deploy --only functions",
    "logs": "firebase functions:log"
  },
  "engines": {
    "node": "20"
  },
  "main": "built/index.js",
  "dependencies": {
    "axios": "^1.6.8",
    "firebase-admin": "^11.8.0",
    "firebase-functions": "^4.9.0"
  },
  "devDependencies": {
    "firebase-functions-test": "^3.1.0",
    "typescript": "^4.9.0"
  },
  "private": true
}

if i am INSIDE functions folder and run npm run serve it works as expected but if i run firebase serve... it only starts the webserver with the current compiled code, any modifications arent reflected and if the code isn't compiled yet it will fail to start

what can i do to fix this?

Answer 1

It's working as expected. firebase serve does not run any sort of compilation or pre-processing on your code. It just uses what's there (perhaps your previously compiled JavaScript).

The reason why npm run serve works as you expect is because your serve script has an explicit instruction to compile your TS:

"serve": "npm run clean-build && npm run build && firebase emulators:start --only functions",

The npm run build part of the script does that compilation (using tsc) before running the emulator.

If you want a single command to run your compile step before firebase serve, maybe you could create a new script for that. Such as:

"firebase-serve": "npm run clean-build && npm run build && firebase serve",