Firebase Cloud Functions触发返回undefined，期望Promise或值如何解决

问题根因 #

该报错的核心原因是Firebase Cloud Functions要求触发器回调必须返回一个Promise或者明确的返回值，你当前代码没有返回Firestore查询的Promise链，函数同步执行到末尾直接返回undefined，就会抛出Function returned undefined, expected Promise or value的错误，即使最终显示状态为ok，也可能出现异步逻辑未执行完成就被回收的问题。

此外代码还存在两个会导致推送发送失败的隐藏问题：

• 嵌套的admin.messaging().sendToDevice()异步调用没有被返回，外层Promise会提前resolve，函数实例可能在推送请求发出前就被销毁
• API参数使用错误：你写的payload格式是admin.messaging().send()方法的入参格式，而sendToDevice方法要求第一个参数传设备token，第二个参数才是通知配置

修正后的代码（保持then链写法） #

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

exports.updateOrderStatus = functions.firestore
  .document("Users/{userId}/Info_Notifications/{notificationId}")
  .onUpdate((change, context) => {
    const newValue = change.after.data();
    const notificationFor = newValue.orderFrom;
    const db = admin.firestore();
    // 这里加return，把整个Promise链返回给Function
    return db.collection("Tokens").doc(notificationFor).get()
      .then((doc) => {
        // 补充doc存在性判断，避免空值报错
        if (!doc.exists) {
          console.log("找不到对应用户的token文档");
          return null;
        }
        const user = doc.data();
        const deviceID = user.id;
        console.log("Device id", deviceID);
        const payload = {
          token: deviceID,
          notification: {
            title: "Test Notification",
            body: "message",
          },
          data: {
            priority: "high",
            timeToLive: "60 * 60* 24",
          },
        };
        // 这里返回send的Promise加入链中，换成send方法适配你写的payload格式
        return admin.messaging().send(payload)
          .then((response) => {
            console.log("推送发送成功", response);
            return true;
          })
          .catch((error) => {
            console.log("Error Sending Notifications", error);
            return false;
          });
      }).catch((error) => {
        console.log("Error in fetching data", error);
        return false;
      });
  });

更易维护的async/await写法参考 #

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

exports.updateOrderStatus = functions.firestore
  .document("Users/{userId}/Info_Notifications/{notificationId}")
  .onUpdate(async (change, context) => {
    try {
      const newValue = change.after.data();
      const notificationFor = newValue.orderFrom;
      const db = admin.firestore();
      const doc = await db.collection("Tokens").doc(notificationFor).get();
      
      if (!doc.exists) {
        console.log("找不到对应用户的token文档");
        return null;
      }
      
      const user = doc.data();
      const deviceID = user.id;
      console.log("Device id", deviceID);
      
      const payload = {
        token: deviceID,
        notification: {
          title: "Test Notification",
          body: "message",
        },
        data: {
          priority: "high",
          timeToLive: "60 * 60* 24",
        },
      };
      
      const response = await admin.messaging().send(payload);
      console.log("推送发送成功", response);
      return true;
    } catch (error) {
      console.log("执行出错", error);
      return false;
    }
  });

内容的提问来源于stack exchange，提问作者jigexi