Send transactional push notifications from a Firebase Cloud Function

Send transactional push notifications from a Firebase Cloud Function.js

function sendPush(uid) {

  // Get the user from Firestore
  const getDeviceTokensPromise = admin.firestore()
  .collection('users').doc(uid).get();

  // Get the User profile from Firebase Auth
  const getUserProfilePromise = admin.auth().getUser(uid);

  Promise.all([getDeviceTokensPromise, getUserProfilePromise])
  .then(function(results) {
    // The array containing all the user's tokens.
    const tokens = Object.keys(results[0].data().notificationTokens);

    // The user profile from Firebase Auth
    const user = results[1];

    // Check if there are any device tokens.
    if (tokens.length === 0) {
      return console.log('There are no notification tokens to send to.');
    }

    // Notification details.
    const payload = {
      notification: {
      title: 'Payment completed!',
      body: `Thank you, ${user.displayName}, we received your payment.`
      }
    };

    // Send notifications to all tokens.
    admin.messaging().sendToDevice(tokens, payload)
    .then(function(response) {
      console.log('Successfully sent push: ', response);
      return response;
    })
    .catch(function(error) {
      console.log('Error sending push:', error);
    });
    
    return results;
  })
  .catch(function(error) {
    console.log('Error retrieving tokens or user details:', error);
  });

}