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Part 2 - Sprinkle in some types

In this part you will rewrite functions from previous part to TypeScript to get some easy write/compile time safety.

Steps:

  • Make sure that TypeScript is installed:
npm install -g typescript
  • Add configuration to package.json (note dependencies and scripts):
{
 "name": "functions",
 "description": "Cloud Functions for Firebase",
 "dependencies": {
   "firebase-admin": "~5.4.0",
   "firebase-functions": "^0.7.0"
 },
 "devDependencies": {
   "typescript": "^2.3.2"
 },
 "scripts": {
   "build": "tsc",
   "deploy": "tsc && firebase deploy --only functions"
 },
 "main": "build/index.js",
 "private": true
}
  • Add tsconfig.json in the same folder as package.json:
 {
    "compilerOptions": {
        "lib": [
            "es6",
            "es2015.promise"
        ],
        "module": "commonjs",
        "noImplicitAny": false,
        "outDir": "build",
        "sourceMap": true,
        "target": "es6"
    },
    "include": [
        "src/**/*.ts"
    ]
}
  • Create src/index.ts file with Firebase imports:
import * as functions from 'firebase-functions'
import * as admin from 'firebase-admin'

admin.initializeApp(functions.config().firebase)
  • Add basic class definitions for tables in the database:
class Rates {
    usd: number
    czk: number
    pln: number
    rub: number
}

class Conversions extends Rates {
    constructor(eur: number) {
        super()
        this.eur = eur
    }

    eur: number
    timestamp: number
}
  • Translate the function testPush to TypeScript:
export let testPush = functions.https.onRequest((req, res) => {
    admin.database().ref('/conversions')
        .push(new Conversions(parseFloat(req.query.eur)))
        .then(snap => { res.status(200).send("done") })
})
  • Build project and check out build/index.js:
npm run-script build
  • Deploy and verify that all fuctions work the same as before:
npm run-script deploy
  • Translate the function convert to TypeScript:
export let convert = functions.database.ref('/conversions/{conversionID}').onWrite(event => {
    var conversion = event.data.val() as Conversions
    // Do not handle already converted values
    if (conversion.timestamp !== undefined) return

    var eur = conversion.eur
    admin.database().ref('/rates').once('value').then(ratesSnapshot => {
        let rates = ratesSnapshot.val() as Rates

        let result = new Conversions(eur)
        result.usd = eur * rates.usd
        result.czk = eur * rates.czk
        result.pln = eur * rates.pln
        result.rub = eur * rates.rub
        result.timestamp = Date.now()

        admin.database().ref('/conversions').child(event.params.conversionID).set(result)
    })
})

Conclusions:

Now if you accidentally make a typo, it will not transpile or even better - editor will highlight an error. Also in more advanced editors you get different levels of code completion that highly improve productivity.

Since we have implemented type safety, let’s go a step further and use Kotlin. It will not only provide same benefits as TypeScript, but also allow code reuse between platforms.

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