使用React Hooks和Context检查电子邮件是否已存在于Firestore的集合中

import React, { createContext, useContext, useState } from 'react';
import firebase from 'firebase/app';
import 'firebase/firestore';

// 初始化Firebase
firebase.initializeApp({
  // 配置你的Firebase项目
});

// 创建一个Context
const FirestoreContext = createContext();

// 创建一个自定义的Hook，用于在组件中获取Firestore实例和检查电子邮件是否存在的方法
export const useFirestore = () => useContext(FirestoreContext);

// 创建一个Context Provider组件，提供Firestore实例和检查电子邮件是否存在的方法
export const FirestoreProvider = ({ children }) => {
  const [firestore] = useState(() => firebase.firestore());

  const checkEmailExists = async (email) => {
    const snapshot = await firestore.collection('users').where('email', '==', email).get();
    return !snapshot.empty;
  };

  return (
    <FirestoreContext.Provider value={{ firestore, checkEmailExists }}>
      {children}
    </FirestoreContext.Provider>
  );
};

import React, { useState } from 'react';
import { useFirestore } from './FirestoreProvider';

const EmailForm = () => {
  const { checkEmailExists } = useFirestore();
  const [email, setEmail] = useState('');
  const [emailExists, setEmailExists] = useState(false);

  const handleEmailChange = (e) => {
    setEmail(e.target.value);
  };

  const handleEmailBlur = async () => {
    const exists = await checkEmailExists(email);
    setEmailExists(exists);
  };

  return (
    <div>
      <input type="email" value={email} onChange={handleEmailChange} onBlur={handleEmailBlur} />
      {emailExists && <span>Email already exists</span>}
    </div>
  );
};

export default EmailForm;