chris esplin

Cloud Functions for Firebase
Cloud Functions for Firebase are Google’s serverless solution for Firebase apps. They can be used as the (R)eactor functions for FIRE Stack app architecture. If you’ve developed with firebase-queue, AWS Lambda or some other Functions-as-a-Service architecture, Cloud Functions for Firebase should feel natural… just a lot slicker and easier to use :)

If you’re wondering where to start… well, read on my friend.

FIRE Stack

FIRE Stack architecture replaces the typical REST API, with its endpoints and HTTP calls, with standalone functions — written by you and running on Google’s infrastructure — that react to changes in your app and can run any Node.js or Java that your heart desires.

As of this writing, there are six types of triggers:

  1. Firebase Realtime Database triggers

  2. Firebase Authentication triggers

  3. Firebase Analytics triggers

  4. Cloud Storage triggers

  5. HTTP triggers

  6. Cloud Pub/Sub triggers

You can read the docs on each of those triggers for the full rundown. They’re not hard to use, although they can be tricky to test. I’m going to start with Authentication and Firebase Realtime Database triggers. If you can get those working, you shouldn’t have trouble with the other event types.

Node Environment

Cloud Functions supports Node.js LTS releases. The current release is v6.9.1, but check the docs to make sure that you’re developing against the freshest-possible version of Node.js.

If you need help jumping between Node.js versions, check out n for fast version switching.

To get started, I’m running $: n 6.9.1 to switch to v6.9.1.

Authentication Triggers

Authentication triggers track creation and deletion of Firebase Authentication users. That’s about it. Here are the examples from the docs.

That’s really all there is to it. is the user data from your newly minted or deleted currentUser JWT (JavaScript Web Token).

If you want to access your Realtime Database, you can’t get it from the event :( Fortunately, functions.config().firebase contains your initialization details, so you can use firebase-admin to create whatever refs you need.

Realtime Database Triggers

This is the trigger that you need for FIRE Stack architecture)

It’s also the most complicated trigger, because of all of the attributes on the event itself. You need to read up on these attributes. I’ll only be summarizing a few here.

First, scan the docs about event properties. Focus on the following:


  • event.params

Next, read a bit more carefully through the docs on DataSnapshot, a.k.a. This is the crux of Realtime Database events. Pay attention to everything, but read the following word-for-word.

  • DeltaSnapshot.adminRef

- DeltaSnapshot.current

- DeltaSnapshot.key

- DeltaSnapshot.previous

- DeltaSnapshot.ref

- DeltaSnapshot.val()

- DeltaSnapshot.toJSON()

- DeltaSnapshot.numChildren()

You’re back already? Have you understood the docs? If so, GREAT! If not, for shame! Go back and read ’em :)

Once you understand the event object, database triggers aren’t tough to figure out. I have an architectural pattern where I like to track user logins. It’s kind of an important metric, and it’s a good opportunity to update the user’s account. I have my client app push data to /queues/current-user/{uid}, something like this…

Then I register a Firebase Function to listen to queues/login/{uid} and do whatever I need.

Use and is a ref with full admin privileges over your entire database. ** **is a ref as well, but is has the same authentication permissions as the user who triggered the event. This is super useful. It enables you to impersonate a user from within your function, security-rules restrictions and all!

Also, if you try to do something “admin-like” from, don’t be surprised when you get weird permission denied errors in your Cloud Functions logs.

Use event.params

In the earlier example I registered my onWrite event like so:

functions.database.ref(‘queues/login/{uid}’).onWrite(event => {…});

Notice the wildcard {uid}. That wildcard ends up as event.params.uid. So if write something to /queues/login/fake-uid-123, then event.params.uid will be ’fake-uid-123'. Pretty simple.

But the plot thickens, because you can do crazy stuff like

functions.database.ref(‘/queues/{queueType}/{uid}’).onWrite(event => {…});

See that! You can use multiple wildcards in a path! I don’t know how many wildcards you can use, and I’ve never used more than two… but go hog-wild and let me know if you find the limits!

Use environment variables!

The docs on environment variables show how you can use firebase-tools to set your functions environment variables from the command line. Basically, you install firebase-tools globally with yarn global add firebase-tools (or npm install -g firebase-tools). Then you use the CLI to do the work.

firebase functions:config:set access-control-lists.admin-users=”,”

Notice that I used kebab case instead of camel case. Functions config does not allow uppercase characters in attribute keys. So accessControlLists.adminUsers, which is what I’d like to type here, will not work!!! 👹

Also notice that I passed in a comma-delimited string. Stick to strings. You can coerce these strings to other data types once you’re in the function… but don’t try to get cute with booleans, numbers or arrays. They’ll all get wrapped in double-quotes.

Require your dependencies within each function

You’ll want to define most of your require statements, i.e., const quiverFunctions = require(‘quiver-functions’), within the function itself. This will run the require function every time the function is run.

This won’t bite you often, but I’ve run into a few situations where my functions wouldn’t deploy until I moved a require call into the function. I suspect it has something to do with how the functions are triggered on Google’s end. If you see error messages when attempting to deploy functions, this tip might help.


I’m using Jasmine for my Node.js tests. It’s easy to get started on your own projects. Just do the following:

I’m using Yarn instead of NPM these days. NPM works almost the same, but let’s be honest, Yarn’s better :) Here are the docs on installing Yarn. If you’re on OS X, you should be using Homebrew for your own sanity. If you’re serious about dev on OS X, and you’re not using Homebrew, take a few minutes to get it set up. Thank me later. Installing Yarn with Homebrew is as easy as brew update && brew install yarn.

  1. Install Jasmine globally: yarn global add jasmine

  2. Install Jasmine in your project: yarn add jasmine

  3. Initialize Jasmin: jasmine init

  4. Edit ./spec/support/jasmine.json to make sure that the spec_dir and spec_files will pick up your tests.

You can run the test in this repo by simply installing and running jasmine at the top-level of the repo. Otherwise, you can cd functions && yarn test to get the same result. Note that you’ll need to copy /functions/config.json.dist to /functions/config.json and edit the file so that it contains your Firebase details. I’m not checking my service-account.json file into source control :)