尝试从Firebase集合中提取数据时出错REACT： TypeError：无法读取未定义的属性（读取“map”）

Question

试图从firebase导入数据时，我被抛出了这个错误：REACT:TypeError:无法读取未定义的属性（读取“map”）。

制定一个项目，监控云功能的运行状况以及它们是否正常工作。任何帮助都将不胜感激。：）

app.js-地图功能app.js{

  45 | </Divider>
  46 | 
  47 | {user ? (
> 48 |   <Card.Group itemsPerRow="4">
     | ^  49 |     {cloudFucntions.map((cloudFunction) => {
  50 |       return (
  51 |         <Cards

}

import "./App.css";
import "semantic-ui-css/semantic.min.css";
import { Container, Divider, Card } from "semantic-ui-react";
import Header from "./components/Header";
import Cards from "./components/Cards/index";
import { useState, useEffect } from "react";
import { AppProvider } from "./Context/Context.js";
import "firebase/compat/auth";
import {} from "firebase/firestore";
import * as FirestoreService from "./components/service/firebase";
import firebase from "@firebase/app-compat";

function App() {
  const [user, setUser] = useState(null);
  const [cloudFucntions, setCloudFucntions] = useState();

  const [setError] = useState();

  useEffect(() => {
    firebase.auth().onAuthStateChanged((user) => {
      setUser(user);

      const unsubscribe = FirestoreService.getCloudFunctionItems(
        (querySnapshot) => {
          const updatedCloundFunctions = querySnapshot.docs.map((docSnapshot) =>
            docSnapshot.data()
          );
          setCloudFucntions(updatedCloundFunctions);
          console.log(updatedCloundFunctions);
        },
        (error) => setError("list-item-get-fail")
      );
      return unsubscribe;
    });
  }, []);

  return (
    <AppProvider>
      <div>
        <Container>
          <Header />

          <Divider horizontal section>
            Cloud Function Monitor
          </Divider>

          {user ? (
            <Card.Group itemsPerRow="4">
              {cloudFucntions.map((cloudFunction) => {
                return (
                  <Cards
                    key={cloudFunction.id}
                    cloudFunctions={cloudFunction}
                  ></Cards>
                );
              })}
            </Card.Group>
          ) : (
            <h2> Please sign in using the button in the top right. </h2>
          )}
        </Container>
      </div>
    </AppProvider>
  );
}

export default App;

firebase.js：

import firebase from "firebase/compat/app";
import "firebase/compat/auth";
import { initializeApp } from "firebase/app";
import {
  getFirestore,
  query,
  orderBy,
  onSnapshot,
  collection,
  getDoc,
  getDocs,
  addDoc,
  updateDoc,
  doc,
  serverTimestamp,
  arrayUnion,
} from "firebase/firestore";

const firebaseConfig = {
  apiKey: "xxx",
  authDomain: "xxx.firebaseapp.com",
  projectId: "dxxxxdata-d1",
  storageBucket: "xxx-reportingdata-d1.appspot.com",
  messagingSenderId: "xxxxxxxx",
  appId: "xxxxxxxx",
  measurementId: "G-xxxxxxx",
};

firebase.initializeApp(firebaseConfig);

const app = initializeApp(firebaseConfig);
const db = getFirestore(app);

export const getCloudFunctionItems = (snapshot, error) => {
  const itemsColRef = collection(db, "cloudFunctionsMonitor");
  const itemsQuery = query(itemsColRef);
  return onSnapshot(itemsQuery, snapshot, error);
};

export const getCloudFunction = (cloudFunctionId) => {
  const cloudDocRef = doc(db, "cloudFunction", cloudFunctionId);
  return getDoc(cloudDocRef);
};

export const auth = firebase.auth();

const provider = new firebase.auth.GoogleAuthProvider();
provider.setCustomParameters({ prompt: "select_account" });

export const signInWithGoogle = () => auth.signInWithPopup(provider);

export default firebase;

卡片/索引。js

import "../../App";
import "semantic-ui-css/semantic.min.css";
import { Icon, Card, Button } from "semantic-ui-react";
import "semantic-ui-css/semantic.min.css";
import React, { Component } from "react";
import "semantic-ui-css/semantic.min.css";

export default class Cards extends Component {
  render() {
    return (
      <Card color={this.props.cloudFunction.functionColor}>
        {/* <h1> lastrunload: {this.propps.app.updatedCloundFunctions}</h1> */}
        <Card.Content>
          <Card.Header>
            {this.props.cloudFunction.cardFunctionHeader}
          </Card.Header>
          <Card.Description>
            {this.props.cloudFunction.cardFunctionDescription}
          </Card.Description>
        </Card.Content>
        <Card.Content extra>
          <Icon name="cog" />
          {this.props.cloudFunction.functionRunTime}
          <br />
          <Icon name="clock" />
          {this.props.cloudFunction.functionLastRun}
          <br />
          <Icon name="angle double down" />
          {this.props.cloudFunction.functionLastInsert}
        </Card.Content>
        <Card.Content extra>
          <div className="ui two buttons">
            <Button basic color={this.props.cloudFunction.functionColor}>
              {this.props.cloudFunction.functionButton}
            </Button>
          </div>
        </Card.Content>
      </Card>
    );
  }
}

Answer 1

添加未定义的检查，然后在未定义上执行. map（），检查然后仅在不为空或未定义时调用，

<Card.Group itemsPerRow="4">
{cloudFucntions && cloudFucntions.map((cloudFunction) => {
  return (
    <Cards
      key={cloudFunction.id}
      cloudFunctions={cloudFunction}
    ></Cards>
  );
})}
</Card.Group>

const unsubscribe = FirestoreService.getCloudFunctionItems(
    (querySnapshot) => {
      const updatedCloundFunctions = querySnapshot && querySnapshot.docs && querySnapshot.docs.map((docSnapshot) =>
        docSnapshot.data()
      );
      setCloudFucntions(updatedCloundFunctions);
      console.log(updatedCloundFunctions);
    },
    (error) => setError("list-item-get-fail")
  );
  return unsubscribe;
});