Triggering Functions

Cloud Functions become truly powerful when they react to events happening in your Firebase services.

1. Firestore Triggers

You can listen to document creation, updates, and deletions.

// Trigger when a new document is created in "messages"
exports.onMessageCreate = functions.firestore
    .document('messages/{messageId}')
    .onCreate((snap, context) => {
      const newValue = snap.data();
      console.log('New message:', newValue.text);
    });

2. Authentication Triggers

Useful for creating user profiles in Firestore immediately after registration.

exports.createUserAccount = functions.auth.user().onCreate((user) => {
  // Logic to add user to Firestore
  return admin.firestore().collection('users').doc(user.uid).set({
    email: user.email,
    createdAt: admin.firestore.FieldValue.serverTimestamp()
  });
});

3. Storage Triggers

Triggered when a file is uploaded or deleted (e.g., to generate thumbnails).

exports.generateThumbnail = functions.storage.object().onFinalize((object) => {
  // Logic to process the image
});