使用NextAuth Firebase适配器报错Cannot access 'app' before initialization

• 初始化顺序错误：你的Firebase客户端配置文件中，调用getAnalytics(app)时app还未执行初始化赋值，app的初始化代码在调用语句之后，触发了变量未初始化的引用错误。
• SDK版本混用：代码同时使用了Firebase v8的命名空间导入语法（import firebase from "firebase/app"）和v9的模块化API语法（import { initializeApp } from "firebase/app"），两种语法不兼容，也会引发后续调用异常。

1. 修正Firebase客户端配置代码 #

统一Firebase SDK写法，调整初始化顺序，避免变量未初始化调用，修正后代码示例如下：

import firebase from "firebase/app";
import "firebase/auth";
import "firebase/firestore";
import "firebase/analytics";

const firebaseConfig = {
  apiKey: process.env.NEXT_PUBLIC_FIREBASE_API_KEY,
  authDomain: process.env.NEXT_PUBLIC_FIREBASE_AUTH_DOMAIN,
  projectId: process.env.NEXT_PUBLIC_FIREBASE_PROJECT_ID,
  storageBucket: process.env.NEXT_PUBLIC_FIREBASE_STORAGE_BUCKET,
  messagingSenderId: process.env.NEXT_PUBLIC_FIREBASE_MESSAGING_SENDER_ID,
  appId: process.env.NEXT_PUBLIC_FIREBASE_APP_ID,
  measurementId: process.env.NEXT_PUBLIC_FIREBASE_MEASURMENT_ID,
};

// 避免重复初始化
if (!firebase.apps.length) {
  firebase.initializeApp(firebaseConfig);
}

const app = firebase.app();
const analytics = firebase.analytics(app);
const firestore = firebase.firestore();

export { firestore };
export default firebase;

2. 简化NextAuth配置代码 #

直接复用Firebase客户端导出的firestore实例，避免重复初始化逻辑：

import NextAuth from "next-auth";
import { FirebaseAdapter } from "@next-auth/firebase-adapter";
import GoogleProvider from "next-auth/providers/google";
import { firestore } from "../../../firebase/FirebaseClient";

export default NextAuth({
  providers: [
    GoogleProvider({
      clientId: process.env.GOOGLE_CLIENT_ID,
      clientSecret: process.env.GOOGLE_CLIENT_SECRET,
    }),
  ],
  adapter: FirebaseAdapter(firestore),
});

额外注意 #

如果你的项目使用Firebase v9模块化版本，需同步升级@next-auth/firebase-adapter到支持v9的对应版本，避免API不兼容问题。

内容的提问来源于stack exchange，提问作者KeoooDev