尝试在Firebase FireStore中创建函数时Javascript Promises错误

Question

so I've been following this 5 part tutorial series as to how notifications can be sent from device to device using Firebase Cloud Storage and the javascript I wrote seems to be incorrect because I keep getting the error that "Each then() should return a value or throw promise/always-return". Can someone tell me as to how I should correct this?

index.js

'use-strict'

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

exports.sendNotification = functions.firestore.document("Users/{user_id}/Notifications/{notification_id}").onWrite((event) => {

  var user_id = event.params.user_id;
  var notification_id = event.params.notification_id;

  //console.log("User ID: " + user_id + " | Notification ID : " + notification_id);

  return admin.firestore().collection("Users").doc(user_id).collection("Notifications").doc(notification_id).get().then(queryResult => {
    var from_user_id = queryResult.data().from;
    var from_message = queryResult.data().message;

    var from_data = admin.firestore().collection("").doc("from_user_id").get();
    var to_data = admin.firestore().collection("Users").doc(user_id).get();

    return Promise.all([from_data, to_data]).then(result => {
      var from_name = result[0].data().name;
      var to_name = result[1].data().name;
      var token_id = result[1].data().token_id;

      console.log("From: " + from_name + " | To : " + to_name);

      var payload = {
        notification : {
          title : "Notification From : " + from_name,
          body : from_message,
          icon : default
        }
      };

      return admin.messaging().sendToDevice(token_id, payload).then(result => {
        console.log("Notification Sent");
      });
    });
  });
});

Apart from the above error I also get a "parsing" error as follows

32:18 error Parsing error: Unexpected token default

Answer 1

"Each then() should return a value or throw promise/always-return"

This indicates that one of your .then 's doesn't return a value (or throw an error)

Here is the culprit:

.then(result => {
    console.log("Notification Sent");
});

So add a return . Now, since console.log return value is undefined and in a function having no return statement there's an implied return undefined

Therefore the code below results in exactly the same behaviour (ie return undefined ), and will prevent that warning message

.then(result => {
    return console.log("Notification Sent");
});

As far as your error regarding default , that's simply because default is a reserved word in javascript (and it's not even declared in your code anyway) - it's like trying to use if or while as a variable name

---

Another potential issue I see in your code is

var from_user_id = queryResult.data().from;
var from_message = queryResult.data().message;

//***                                                vvvvvvvvvvvvvv
var from_data = admin.firestore().collection("").doc("from_user_id").get();
var to_data = admin.firestore().collection("Users").doc(user_id).get();

Should that be .doc(from_user_id) - otherwise, what is the point of var from_user_id = queryResult.data().from;

---

And finally, as an aside, I see that you are nesting your promises rather than chaining them. One benefit of promises is you can avoid the "callback pyramid of hell/doom"

Your code could be written like below instead which avoids the "pyramid" - there's also some other ES6/ES7+ tricks in there so that queryResult.data() and to_data.data() only needs to be called once

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

exports.sendNotification = functions.firestore.document("Users/{user_id}/Notifications/{notification_id}").onWrite((event) => {

    const user_id = event.params.user_id;
    const notification_id = event.params.notification_id;

    return admin.firestore().collection("Users").doc(user_id).collection("Notifications").doc(notification_id).get()
    .then(queryResult => {
        const {from:from_user_id, message:from_message} = queryResult.data();

        const from_data = admin.firestore().collection("").doc(from_user_id).get();
        const to_data = admin.firestore().collection("Users").doc(user_id).get();

        return Promise.all([from_data, to_data, from_message]); // added from_message so it's available in the next .then
    })
    .then(([from_data, to_data, from_message]) => { // added from_message
        const from_name = from_data.data().name;
        const {name:to_name, token_id} = to_data.data();

        console.log("From: " + from_name + " | To : " + to_name);

        const payload = {
            notification : {
                title : "Notification From : " + from_name,
                body : from_message,
                icon : 'default'
            }
        };

        return admin.messaging().sendToDevice(token_id, payload);
    })
    .then(result => {
        return console.log("Notification Sent");
    });
});

Answer 2

You are using the reserved keyword default which you cannot use. I guess you meant to represent this as a string, eg "default"