Building an API using Firebase Functions for cheap

When I am working on personal projects, I often find the need to setup an API that serves up data to my app or webpages.  I get frustrated when I end up spending too much time on hosting and environment issues.

These days what I end up doing is hosting the API using 

The official name is Cloud Functions for Firebase.  In this article, I am going to call it Firebase Functions.
This is mostly to distinguish it from Google's 

 serverless functions-as-a-service: Cloud Functions.  You can read more about the 

While I'm not going to write a mobile app in this article, I like to use Firebase Functions because:

If all this isn't confusing enough, Google is rolling out a new version of Cloud Functions called 

So in order to move forward, let's identify our working assumptions:

After all this is complete, you should have a single file called 

 directory is where we'll write our API code.

Congrats, you have Firebase Functions working on your local system! To exit the emulator, just type 'Ctrl-C' at your terminal window.

This is all very exciting.  Let's push our new "hello world" function into the cloud.  From the
command line type:

The output should look similar, but not exactly to:

=== Deploying to 'newline-test1'...

i  deploying functions
i  functions: ensuring required API cloudfunctions.googleapis.com is enabled...
i  functions: ensuring required API cloudbuild.googleapis.com is enabled...
⚠  functions: missing required API cloudbuild.googleapis.com. Enabling now...
✔  functions: required API cloudfunctions.googleapis.com is enabled
✔  functions: required API cloudbuild.googleapis.com is enabled
i  functions: preparing functions directory for uploading...
i  functions: packaged functions (50.13 KB) for uploading
✔  functions: functions folder uploaded successfully
i  functions: creating Node.js 16 function helloWorld(us-central1)...
✔  functions[helloWorld(us-central1)] Successful create operation.
Function URL (helloWorld(us-central1)): https://us-central1-newline-test1.cloudfunctions.net/helloWorld
i  functions: cleaning up build files...

✔  Deploy complete!

Project Console: https://console.firebase.google.com/project/newline-test1/overview

 we should get the 'Hello from Firebase!' message.  Exciting!
Do you see how easy it is to create Firebase Functions?

We've done all the hard part of setting up our local environment and the Firebase project.  Let's jump
into creating an API using 

const functions = require('firebase-functions')

const app = require('express')() // Note the shortcut here to get app initialized.  The extra ()

const testHelloWorld = async (req, res) => {
    res.send('Hello World!')
}

const testJSON = async (req, res) => {
    res.json({ message: 'You are awesome because you created an API', awesomeLevel: 9000 })
}

app.get('/', testHelloWorld)
app.get('/testJSON', testJSON)

exports.api = functions.https.onRequest(app)

You can load up your api locally.  Note the URL link on the emulator is a little different -- it should
have 'api' added at the end like:

http://localhost:5001/newline-test1/us-central1/api

You should see our 'Hello World' message.  Now for more fun, add '/testJSON' to the end of your link.
You should see the browser return back JSON data that our API has sent:

Note that when you try to deploy, Firebase is smart enough to detect that major changes to the URL structure
have occurred.  You'll need to verify that you did indeed make these changes and everything is ok.
Since this is a trivial function, you can type 

.  Firebase will delete the old function we deployed
earlier and create a new one.

Once that completes, try to load the link and validate your API is now working!

This article has walked you through the basics of using Firebase Functions to host your own API.

The process of writing and creating a full featured API is beyond the scope of this article.
There are many resources out there to help with this task, but I hope you'll think about Firebase
Functions next time you are starting a project.

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Amelia Wattenberger

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