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Part 1 - A basic project setup

In this part you will create very simple Firebase Functions project with two functions:

  • testPush - function with https trigger that will be used to simulate client requests that write data into Realtime Database.
  • convert - function with database onWrite trigger that will do conversion and write data back into database.

Steps:

  • Create a project in the Firebase console
https://console.firebase.google.com/
  • Put the rates node into the database:
"rates" : {
   "usd" : 1.175,
   "czk" : 25.88,
   "pln" : 4.303,
   "rub" : 68.52
}
  • Install and set up the Firebase CLI tools (if not yet done):
npm install -g firebase-tools
firebase login
  • Initialize the Firebase project:
firebase init functions
  • Open index.js (this is where functions are added) and write testPush function for later use:
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

exports.testPush = functions.https.onRequest((req, res) => {
   admin.database().ref('/conversions')
       .push({ eur: parseFloat(req.query.eur) })
       .then(snap => { res.status(200).send("done") })
})
  • Deploy this function with the CLI tools:
firebase deploy --only functions
  • Trigger the test function to check if it works by calling (project link should be available in console):
https://<project-link>/testPush?eur=100
  • Add the function that does the conversion:
exports.convert = functions.database.ref('/conversions/{conversionID}').onWrite(event => {
    const conversion = event.data.val()
    // Do not handle already converted values
    if (conversion.timestamp !== undefined) return

    const eur = conversion.eur
    admin.database().ref('/rates').once('value').then(ratesSnapshot => {
        const rates = ratesSnapshot.val()
        const result = {
            eur: eur,
            usd: eur * rates.usd,
            czk: eur * rates.czk,
            pln: eur * rates.pln,
            rub: eur * rates.rub,
            timestamp: Date.now()
        }
        admin.database().ref('/conversions').child(event.params.conversionID).set(result)
    })
})

Conclusions:

By now you should have at least a basic understanding how Firebase Functions are implemented. But there is a small issue - JavaScript is very susceptible to typos and undefined is not a function type errors. In case of convert function typo in timestamp check might cause infinite recursive function calls and cost you a lot of money.

To make it a bit more safe, in Part 2 we are going to introduce some type safety.

Links: