Trigger Functions Directly

In the Introduction to Cloud Functions lesson, we mentioned that Cloud Functions could either be called directly or triggered in response to an event. Since we have a brief overview of how Cloud Functions work, let’s go deeper to see ways in which we can directly invoke our Cloud Functions.

There are three ways we can call Firebase Cloud Functions directly, each with its unique operation and usage. These methods are as follows:

• Schedule a Cloud Function to run at specific times or intervals.
• Trigger a function in response to an HTTP request.
• Calling a Cloud Function directly from the Firebase App. This means calling it from the client.

For this course, we’ll focus on triggering functions via HTTP requests and calling functions directly from an application.

Trigger via HTTP requests

To write an HTTP request function, we must use the onRequest handler that exists on the functions.https object. Just like in an Express application, it takes two object parameters, request and response. The request object represents the properties of the request sent by the client, while the response object provides a way to send a response back to the client.

We can terminate HTTP functions with either of three following methods on the response object— .send(), .redirect(), or .end(). We already saw an example of a simple HTTP request function in the previous lesson. Now, let’s write something more complex: