extension-to-functions-codebase

SKILL.md

Extension to Functions Codebase & npm Package Migration

Overview

Migrates a Firebase Extension into either:

A local Cloud Functions codebase (functions/src/ for app integration).

A publishable npm package (reusable open-source package exporting V2
functions).

Leverages native Cloud Functions features (declarative IAM, Parameterized
Config, SDK Lifecycle Hooks) and modernizes 1st Gen triggers to 2nd Gen using
the Destructuring Compatibility Shim.

Target Migration Workflows

Target A: Local Functions Codebase (End-User App Integration)

Output: Code under functions/src/. Config in .env.

Deployment: firebase deploy --only functions.

Target B: Publishable npm Package / Shareable Package

Output: Reusable npm package exporting V2 functions.

Configuration: package.json specifying exports map,
engines: { "node": ">=22" }, and
peerDependencies: { "firebase-functions": ">=6.0.0" }.

Usage: Consumers install package and re-export functions in index.ts
(export * from "<package-name>").

Core Rules & Constraints

1. Declarative IAM & APIs (Zero-Local-Overhead)

Use native SDK declarations instead of manual gcloud scripts or console
instructions:

Use requiresRole("roles/...") for required GCP IAM permissions.

Use requiresAPI("service.googleapis.com", "Description") for Google APIs.

2. Global Parameter Access Restriction

Never call .value() at top-level module load scope.

Initialize global SDK instances inside onInit() or lazy getters:
import { defineString } from "firebase-functions/params";
import { onInit } from "firebase-functions/v2";

const dataset = defineString("DATASET_ID");
let client: BigQuery;

onInit(() => {
  client = new BigQuery({ datasetId: dataset.value() });
});

3. V2 Concurrency & Cost Parity

V2 enables concurrency (up to 80 requests). To preserve V1 single-concurrency
pricing, set cpu: "gcf_gen1".

Step-by-Step Migration Execution

Step 1: Inventory Extension Resources

extension.yaml:

params → defineString, defineInt, defineBoolean, defineSecret.

apis → requiresAPI(...).

roles → requiresRole(...).

lifecycleEvents → afterFirstDeploy & afterRedeploy.

resources → Upgrade 1st Gen triggers to 2nd Gen (onDocumentWritten,
onTaskDispatched, onRequest).

Files & Scripts: Preserve devDependencies, test framework (jest), and
test scripts.

Step 2: Configure package.json

Set name: "<package-name>", engines: { "node": ">=22" }.

Set peerDependencies:
"peerDependencies": {
  "firebase-admin": "^11.0.0 || ^12.0.0",
  "firebase-functions": ">=6.0.0"
}

Configure exports map targeting ESM/CommonJS and TypeScript declarations
(lib/index.js, lib/index.d.ts).

Step 3: Upgrade Triggers from V1 to V2

Firestore: Use onDocumentWritten from firebase-functions/v2/firestore.

Tasks: Use onTaskDispatched from firebase-functions/v2/tasks. Remove
EXT_INSTANCE_ID when enqueueing tasks.

HTTP: Use onRequest from firebase-functions/v2/https.

Apply Destructuring Compatibility Shim ({ change, context },
{ snapshot, context }) where legacy 1st Gen handlers expect
(change, context).

Step 4: Convert Lifecycle Events

Map extension lifecycle events to SDK lifecycle hooks in src/index.ts:

onInstall → afterFirstDeploy({ task: { function: "initTask" } })

onUpdate / onConfigure →
afterRedeploy({ task: { function: "setupTask" } })

Step 5: Package README & Export Instructions

Generate README.md containing:

Installation instructions (npm install).

Re-export snippet (export * from "<package-name>").

Parameterized Configuration .env reference table.

What Changed (Extension vs Package) comparison table.

Reminder: NEVER execute npm publish.