返回的函数未定义，预期的承诺或价值

问题描述

限时删除！！

我在firebase上触发简单的数据库触发器，然后它会显示如下错误:函数返回了不确定的，期望的承诺或价值"

Whern i fire Simple database trigger on firebase,then it will shows Error like this :"Function returned undefined, expected Promise or 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 ";
});

推荐答案

如果函数中没有异步工作要做，只需return null.返回字符串在Cloud Functions中没有任何意义.如果您出于某些原因需要退还承诺，只需return Promise.resolve().

If you don't have any asynchronous work to do in a function, just return null. Returning a string doesn't have any meaning in Cloud Functions. If you need to return a promise for some reason, just return Promise.resolve().

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