函数返回了未定义的，预期的Promise或值Firebase日志错误 [英] Function returned undefined, expected Promise or value Firebase log error

问题描述

我正在尝试使用firebase-function和node.js在我的应用程序上添加推送通知，并且一切正常，就像我从发件人处收到通知一样.但我唯一关心的是日志给了我这个错误

Im trying to add a push notification on my app using firebase-function and node.js and all its all working fine, like I got notification from the sender. but my only concern is that the log gave me this error

Function returned undefined, expected Promise or value 

这是我的代码:

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

exports.sendNotification = functions.database.ref('/notifications/{user_id}/{notification_id}').onWrite((change, context) => {

    const user_id = context.params.user_id;
    const notification_id = context.params.notification_id;

    console.log('We have a notification : ', user_id);

    const afterData = change.after.val();

    if (!afterData){
        return console.log('A notification has been deleted from the database', notification_id);
    }

    const fromUser = admin.database().ref(`/notifications/${user_id}/${notification_id}`).once('value');
    return fromUser.then(fromUserResult => {

        const from_user_id = fromUserResult.val().from;


        console.log('You have a new notification from: ', from_user_id);

        const deviceToken = admin.database().ref(`/Users/${user_id}/device_token`).once('value');

        return deviceToken.then(result => {

            const token_id = result.val();

            const payload = {
                notification: {
                    title: "New Friend Request",
                    body: "You've received a new Friend Request",
                    icon: "default"
                }
            };

            return admin.messaging().sendToDevice(token_id, payload).then(response => {
                console.log('This was the notification feature');
            });

        });

    });

});

我应该在这里返回什么地方?我目前正在使用最新的Firebase CFM版本1.0

what should I return here and where it will be place? I am currently using the latest firebase CFM version 1.0

推荐答案

此行可能导致错误消息:

This line could be causing the error message:

return console.log('A notification has been deleted from the database', notification_id);

单击此行时，实际上是从函数中返回undefined，因为这是console.log()返回的结果.相反，您应该只在日志后return null.

When this line is hit, you're effectively returning undefined from the function, because that's what console.log() returns. Instead, you should just return null after the log.

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