Firebase | Testing Firebase Cloud Function Locally with Cloud Function Emulator

Firebase CLI provides a cloud function emulator which can be used to run the Firebase Cloud Function locally before deploying to production. Following are the types of functions which can be emulated.

  • HTTP functions
  • Callable functions
  • Background functions triggered from Authentication, Realtime Database, Cloud Firestore, and Pub/Sub.

We will test a simple http function which we created in the last post.

Creating a Cloud Function Using Firebase CLI and TypeScript.

Following are the steps we will follow:

Install or Update the Firebase CLI

Firebase emulator is included in Firebase CLI, so we need to install it, or update it to the latest version.

npm install -g firebase-tools

Setting Up Admin Credentials for Emulated Functions

If your cloud function requires interaction with Google API or Firebase API via the Firebase Admin SDK then you may need to setup the admin credentials.

Go to the Service Accounts in Google Cloud Platform, under your project.

Select the service account row with Name “App Engine default service account“, and click on Actions button at the right end.

Select Manage Keys.

Click on Add Key drop down button.

Select Create new key.

This will open a modal window.

Choose JSON, from the available key types. This will generate and download the key in json file with key details.

JSON key file will look like following, values are omitted here.

{
  "type": "",
  "project_id": "",
  "private_key_id": "",
  "private_key": "",
  "client_email": "",
  "client_id": "",
  "auth_uri": "",
  "token_uri": "",
  "auth_provider_x509_cert_url": "",
  "client_x509_cert_url": ""
}

Set Google Application Credentials to the JSON file path.

This is required to authenticate to Google API or Firebase API from Firebase Admin SDK.

Execute following from project’s root directory. 

set GOOGLE_APPLICATION_CREDENTIALS=path\to\key.json

Run the Firebase Emulator

Now we are ready to start the emulator.

Start the emulator by following command

firebase emulators:start

Emulator will be started and will provide you the function URL.

Call Function URL

Click on provide function URL, and you will receive the response from your function.

Great! We are able to run function locally.

Firebase Emulator UI

You will also be presented with Emulator UI URL.

Open the emulator UI URL in the browser.

In the Emulator screen you will be able to see all the different types of emulators.

You can navigate to Logs, to see any logging by function.

Modify and Test Local Cloud Function

Now let’s update the function.

Change the function response message.

Build the function again, and execute the following from functions folder.

npm run build

Reload the function URL provide by the running emulator and you will see updated response from local function.

When you are happy, you can deploy the function to Firebase as explained in this post.

Firebase | Creating a Cloud Function Using Firebase CLI and TypeScript

Conclusion

The Firebase emulator, which is included in the Firebase CLI, let’s us test the function locally before deploying to the cloud.

In this post we started with installing Firebase CLI and then we setup the Google Account Credential. Google Account Credential requires a JSON file with private key, which was generated in the Google Cloud Platform. Then we started the Firebase emulator and browsed the local function URL and received response from the local function.

Hope you liked this, please share your feedback or any query.

Leave a comment