better-firebase-functions skill

This skill provides complete knowledge for implementing and configuring better-firebase-functions (BFF) in any Firebase Cloud Functions project.

What BFF does

BFF replaces manual function imports with automatic discovery + cold-start optimization. Without BFF, every function module loads on every cold start. With BFF, only the one module matching the currently-invoked function loads.

Runtime behaviour at a glance:

• FUNCTION_TARGET / FUNCTION_NAME / K_SERVICE set → cold-start mode: load one matching module only
• None set → deployment mode: load all modules so Firebase CLI can discover triggers
• BFF_BUILD_DISCOVERY=1 set → build-discovery mode: scan files, return metadata, load zero modules

---

Installation

# Core library (always required)
npm install better-firebase-functions

# Optional bundler plugins (pick one or none)
npm install -D better-firebase-functions-esbuild esbuild
npm install -D better-firebase-functions-webpack webpack
npm install -D better-firebase-functions-rollup rollup

---

Entry point setup

The entry point is the single source of truth for all BFF configuration. Write it once — the bundler plugins inherit it automatically.

CJS (most common)

// src/index.ts
import { exportFunctions } from 'better-firebase-functions';

exportFunctions({
  __filename,
  exports,
  functionDirectoryPath: './functions',  // relative to src/index.ts
  searchGlob: '**/*.func.js',            // matches compiled .js files at runtime
});

ESM

// src/index.mjs
import { exportFunctionsAsync } from 'better-firebase-functions';

export default await exportFunctionsAsync({
  __filename: import.meta.filename,
  exports: {},
  functionDirectoryPath: './functions',
  searchGlob: '**/*.func.js',
});

---

Function file structure

Each trigger file exports its trigger as the default export:

// src/functions/auth/on-create.func.ts
import { auth } from 'firebase-functions';

export default auth.user().onCreate(async (user) => {
  console.log('new user', user.uid);
});

// src/functions/http/get-user.func.ts
import { onRequest } from 'firebase-functions/v2/https';

export default onRequest(async (req, res) => {
  res.json({ ok: true });
});

Naming rules (default, customizable):

File path	Firebase function name
functions/on-create.func.ts	onCreate
functions/auth/on-create.func.ts	auth-onCreate
functions/http/get-user.func.ts	http-getUser
functions/http/api/list-users.func.ts	http-api-listUsers

Dashes create Firebase function groups, enabling firebase deploy --only functions:auth.

---

searchGlob convention

The glob must match files as they exist at runtime (after TypeScript compilation):

// ✅ Correct — matches compiled .js files at runtime
searchGlob: '**/*.func.js'

// ✅ Also fine — if you use tsx / ts-node at runtime
searchGlob: '**/*.func.ts'

// ✅ BFF defaults — matches both
searchGlob: '**/*.{js,ts}'

When bundler plugins are used, BFF automatically expands .js → .{js,ts} so build-time discovery finds TypeScript source files. The runtime glob remains .js.

---

tsconfig / build setup

Typical tsconfig.json for a Firebase project using BFF:

{
  "compilerOptions": {
    "module": "commonjs",
    "target": "ES2020",
    "lib": ["ES2020"],
    "strict": true,
    "esModuleInterop": true,
    "outDir": "lib",
    "rootDir": "src",
    "sourceMap": true,
    "skipLibCheck": true
  },
  "include": ["src"],
  "exclude": ["lib", "node_modules"]
}

With outDir: "lib" and rootDir: "src", your firebase.json should point to lib/index.js and package.json#main should be lib/index.js.

---

Configuration options

All options are optional except __filename and exports.

Option	Type	Default	Description
__filename	string	—	Required. Node's __filename
exports	object	—	Required. Node's exports / module.exports
functionDirectoryPath	string	'./'	Directory of trigger files, relative to entry point
searchGlob	string	'**/*.{js,ts}'	Glob matching trigger files at runtime
funcNameFromRelPath	function	built-in	Custom name generator: (relPath: string) => string
extractTrigger	function	mod?.default	Extract trigger from loaded module
__dirname	string	derived from __filename	Override base directory for discovery
enableLogger	boolean	false	Log discovery and module-load timing
logger	object	console	Custom logger with time, timeEnd, log
exportPathMode	boolean	false	Export file paths instead of triggers (debugging)

---

Bundler plugin setup (optional, takes optimization further)

Bundler plugins produce one independently bundled file per function. No duplicate config is needed — the plugin executes the entry point in build-discovery mode and inherits all settings.

esbuild (recommended for simplicity)

// build.ts (run with: npx tsx build.ts)
import { buildFunctions } from 'better-firebase-functions-esbuild';
import { resolve } from 'path';

await buildFunctions({
  entryPoint: resolve(__dirname, 'src/index.ts'),
  outdir: resolve(__dirname, 'lib'),
  target: 'node20',
  // external: true  ← default: auto-reads from package.json
});

Add to package.json:

{
  "scripts": {
    "build": "tsx build.ts"
  }
}

webpack

// webpack.config.ts
import { resolve } from 'path';
import { BffWebpackPlugin } from 'better-firebase-functions-webpack';

export default {
  target: 'node',
  mode: 'production',
  entry: resolve(__dirname, 'src/index.ts'),
  output: {
    path: resolve(__dirname, 'lib'),
    libraryTarget: 'commonjs2',
  },
  resolve: { extensions: ['.ts', '.js'] },
  module: {
    rules: [{ test: /\.ts$/, use: 'ts-loader', exclude: /node_modules/ }],
  },
  plugins: [
    new BffWebpackPlugin({
      entryPoint: resolve(__dirname, 'src/index.ts'),
    }),
  ],
};

Rollup

// rollup.config.ts
import { resolve } from 'path';
import { bffRollupPlugin, bffRollupOutput } from 'better-firebase-functions-rollup';

export default {
  input: resolve(__dirname, 'src/index.ts'),
  output: bffRollupOutput({ dir: resolve(__dirname, 'lib') }),
  external: ['firebase-admin', 'firebase-functions'],
  plugins: [
    bffRollupPlugin({ entryPoint: resolve(__dirname, 'src/index.ts') }),
  ],
};

Fallback: manual discovery overrides

If the entry point cannot be executed by tsx at build time, pass overrides manually:

new BffWebpackPlugin({
  entryPoint: resolve(__dirname, 'src/index.ts'),
  functionDirectoryPath: './functions',
  searchGlob: '**/*.func.js',
  funcNameFromRelPath: myCustomNamer,
})

---

Custom naming functions

If the default funcNameFromRelPathDefault does not fit your structure, pass a custom function. Important: the same function must be used at runtime (in the entry point) and at build time (the plugin inherits it from the entry point automatically).

// Example: all functions at top level, no group prefix
exportFunctions({
  __filename,
  exports,
  funcNameFromRelPath: (relPath) => {
    const filename = path.basename(relPath);
    return filename.replace(/\.(func\.)?(js|ts)$/, '').replace(/-([a-z])/g, (_, c) => c.toUpperCase());
  },
});

---

Common pitfalls

searchGlob targets .ts but runtime compiled output is .js

Symptom: Functions deploy fine but are empty / not registered at runtime.

Fix: Use **/*.func.js (or whatever compiled extension), not .ts, in searchGlob. If using tsx/ts-node in production, .ts is fine.

Custom funcNameFromRelPath in entry point but not in bundler config

This is no longer an issue with the current build-discovery approach — the plugin executes the entry point and inherits the same function. But if you fall back to manual overrides, make sure both sides match.

Gen 2 / Cloud Run: Function 'x' is not defined in the provided module

Cloud Run lowercases service names. BFF canonicalizes both sides before comparing, so this should be handled automatically. If you still see this error:

1. Check FUNCTION_TARGET is being set by the Functions Framework (it takes precedence)
2. Set enableLogger: true and check which name BFF is searching for

Bundler plugin: did not expose __bff_discovery

BFF needs tsx to require the TypeScript entry point at build time. Install it:

npm install -D tsx

Or pass manual overrides as a fallback (see above).

---

Environment variables (read by BFF)

Variable	When set	BFF behaviour
FUNCTION_TARGET	Gen 2 / Functions Framework	Load the single module whose derived name matches
FUNCTION_NAME	Gen 1, some Gen 2	Same as above; last path segment extracted if full resource path
K_SERVICE	Cloud Run (Gen 2)	Same as above; case-normalized before matching
none of the above	During firebase deploy	Load all modules (deployment mode)
BFF_BUILD_DISCOVERY=1	Set by bundler plugins	Scan files, register discovery metadata, load zero modules

---

Verification checklist

Before deploying, verify:

• __filename and exports are passed to exportFunctions()
• searchGlob matches compiled output (.js) unless running TypeScript natively
• Each trigger file has export default <trigger>
• functionDirectoryPath is correct relative to the entry point
• If using a bundler plugin: entry point can be required by tsx, or manual overrides are provided
• firebase.json source points to the directory containing package.json for the functions codebase
• package.json#main in the functions directory points to the compiled entry point

---

Example directory layout

my-firebase-project/
  functions/
    src/
      index.ts                           ← entry point (exportFunctions call here)
      functions/
        auth/
          on-create.func.ts              ← exports as auth-onCreate
          on-delete.func.ts              ← exports as auth-onDelete
        http/
          get-user.func.ts               ← exports as http-getUser
          create-user.func.ts            ← exports as http-createUser
        payments/
          process-webhook.func.ts        ← exports as payments-processWebhook
    lib/                                 ← compiled output (tsc outDir)
    package.json
    tsconfig.json
  firebase.json

firebase.json:

{
  "functions": {
    "source": "functions"
  }
}

functions/package.json:

{
  "main": "lib/index.js",
  "engines": { "node": "20" },
  "dependencies": {
    "better-firebase-functions": "^7.0.0",
    "firebase-admin": "^12.0.0",
    "firebase-functions": "^6.0.0"
  }
}