异步 Firebase 云 Function 触发器 - 在 catch 块上返回什么？

Question

I have written the trigger below and I'm not sure what I should return in case a catch block is called. I know that Firebase docs say that triggers should always return a Promise ...

exports.sendPushNotificationForNewMessage = functions.firestore.document("messages/{messageId}").onCreate(async (snap, context) => {
      const message = snap.data()
      const chatRoomId = message.chatRoomId
      const senderId = message.user.id
      const senderUsername = message.user.username

      try {
        const chatRoom = await admin.firestore().collection("chatRooms").doc(chatRoomId).get()
        const receiverId = chatRoom.data().userIds.find(userId => userId != senderId)

        const receiver = await admin.firestore().collection("users").doc(receiverId).get()
        const deviceToken = receiver.data().deviceToken

        if (deviceToken) {
          const payload = {
            notification: {
              title: "popster",
              body: `New DM from ${senderUsername} 💬`,
              badge: "1",
              sound: "pop.m4a"
            },
            data: {
            }
          }
          console.log(payload);
          return admin.messaging().sendToDevice(deviceToken, payload)
        } else {
          return null
        }
      } catch (error) {
        return null
      }
})

Answer 1

The async function wraps your response in a Promise so here your return type is Promise<MessagingDevicesResponse | null> Promise<MessagingDevicesResponse | null> and that will terminate the Cloud Function .

I'm not sure what I should return in case a catch block is called.

Background functions do not return any value/error to client so you can just return null; .

Also checkout this Firecast for more information.