Firebase Functions Interop Library for Dart

Build Status

This library provides JS bindings for Firebase Functions Node SDK. It also exposes a convenience layer to simplify writing Cloud Functions applications in Dart.

Please note that it's currently a proof-of-concept-preview version so it lacks many features, tests and documentation. But, it's already fun to play with!


Make sure you have Firebase CLI installed as well as a Firebase account and a test app. See Getting started for more details.

1. Create a new project directory and initialize functions:

$ mkdir myproject
$ cd myproject
$ firebase init functions

This creates functions subdirectory in your project's root which contains standard NodeJS package structure with package.json and index.js files.

2. Initialize Dart project

Go to functions subfolder and add pubspec.yaml with following contents:

name: myproject_functions
description: My project functions
version: 0.0.1

  sdk: '>=1.20.1 <2.0.0'

  # Firebase Functions bindings
  firebase_functions_interop: ^0.0.3
  # Node bindings required to compile a nice-looking JS file for Node.
  # Also provides access to globals like `require` and `exports`.
  node_interop: ^0.0.4

  - $dart2js
  - node_interop # This transformer must go after $dart2js

Then run pub get to install dependencies.

3.1 Write a Web function

Create bin/index.dart and type in something like this:

import 'package:firebase_functions_interop/firebase_functions_interop.dart';

void main() {
  var httpsFunc = firebaseFunctions.https.onRequest((request, response) {
    response.send('Hello from Firebase Functions Dart Interop!');

  exports.setProperty('helloWorld', httpsFunc);

Copy-pasting also works.

3.2 Write a Realtime Database Function (optional)

Update bin/index.dart with following:

void main() {
  // ...Add after helloWorld function...

  // This implements makeUppercase function from the Getting Started tutorial:
  var dbFunc = firebaseFunctions.database
      .onWrite((event) {
    String original =;
    print('Uppercasing $original');
    String uppercase = original.toUpperCase();
  exports.setProperty('makeUppercase', dbFunc);

4. Build your function(s)

Building functions is as simple as running pub build. Note that Pub by default assumes a "web" project and only builds web folder so we need to explicitly tell it about bin:

$ pub build bin

5. Copy and deploy

The result of pub build is located in build/bin/index.dart.js. Replace default index.js with the built version:

$ cp build/bin/index.dart.js index.js

Deploy using Firebase CLI:

$ firebase deploy --only functions

6. Test it

You can navigate to the new HTTPS function's URL printed out by the deploy command. For the Realtime Database function, login to the Firebase Console and try changing values under /messages/{randomValue}/original.


Firebase SDK provides a way to set and access environment variables from your Firebase functions.

Environment variables are set using Firebase CLI, e.g.:

firebase functions:config:set some_service.api_key="secret" some_service.url=""

For more details see

To read these values in a Firebase function use firebaseFunctions.config():

import 'package:firebase_functions_interop/firebase_functions_interop.dart';

void main() {
  var httpsFunc = firebaseFunctions.https.onRequest((request, response) {
    var apiKey = firebaseFunctions.config().get('some_service.api_key');
    var url = firebaseFunctions.config().get('some_service.url');
    // make API call to some_service...
    response.send('Hello from Firebase Functions Dart Interop!');

  exports.setProperty('helloWorld', httpsFunc);

Features and bugs

Please file feature requests and bugs at the issue tracker.


Interop library for Firebase Functions NodeJS SDK. [...]