更改此内容：

exports.pushNotification = functions.database.ref('/messages').onWrite( event => {

const message = event.data.val();
const user = event.data.val();
});

到此：

exports.pushNotification = functions.database.ref('/messages').onWrite(( change,context) => {

const message = change.after.val();
});

请检查：

https://firebase.google.com/docs/functions/beta-v1 -diff＃realtime-database

云功能已更改，现在 onWrite 有两个参数更改和上下文

The cloud functions were changed and now onWrite has two parameters change and context

更改在之前有两个属性，在之后有，并且每个属性都是 DataSnapshot 使用此处列出的方法：

The change has two properties before and after and each of these is a DataSnapshot with the methods listed here:

https://firebase.google.com/docs/reference/admin/node/admin.database.DataSnapshot