函数返回undefined，预期Promise或value

Question

Whern i fire firebase上的简单数据库触发器， 然后它将显示如下错误： “函数返回未定义，预期的Promise或value”

const firebase=require('firebase-admin');

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

exports.helloNotification = functions.database.ref('/users').onWrite(event => {

 return "A Notification has been deleted from the database ";
});

Answer 1

如果您没有在函数中执行任何异步工作，只需return null。返回字符串在云函数中没有任何意义。如果您出于某种原因需要退回承诺，请return Promise.resolve()。

Answer 2

如果您只想让错误消失，您可以只是

return new Promise((resolve, reject) => {
    resolve("A Notification has been deleted from the database ")
})

但是在这里返回一个字符串是没有意义的。

如果它只是用于测试你可以

console.log("A Notification has been deleted from the database ")

代替。

Answer 3

进行一些更改

代替return语句写 console.log（＆＃39; ...＆＃39;）;

在代码顶部添加＆＃39;使用严格＆＃39;

编写 admin 而不是 firebase 来初始化应用

代码看起来像

'use strict'
const firebase=require('firebase-admin');

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

exports.helloNotification = functions.database.ref('/users').onWrite(event => {

 console.log('A Notification has been deleted from the database');
});