エミュレーター作成

エミュレーター初期化実行

$ firebase init emulators

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     ######    ##  ########  ######   ########  #########  ######  ######
     ##        ##  ##    ##  ##       ##     ## ##     ##       ## ##
     ##       #### ##     ## ######## ########  ##     ##  ######  ########

You're about to initialize a Firebase project in this directory:

  /xxxx/xxxx/emulator

プロジェクト設定

=== Project Setup

First, let's associate this project directory with a Firebase project.
You can create multiple project aliases by running firebase use --add, 
but for now we'll just set up a default project.

? Please select an option: 
  Use an existing project 
  Create a new project 
  Add Firebase to an existing Google Cloud Platform project 
❯ Don't set up a default project

デフォルトプロジェクト設定: 省略（結局後で設定してます・・）

? Please select an option: Don't set up a default project

エミュレーター選択: Database Emulator

=== Emulators Setup
? Which Firebase emulators do you want to set up? Press Space to select 
emulators, then Enter to confirm your choices. (Press <space> to select, 
<a> to toggle all, <i> to invert selection, and <enter> to proceed)
 ◯ Authentication Emulator
 ◯ Functions Emulator
 ◯ Firestore Emulator
❯◉ Database Emulator
 ◯ Hosting Emulator
 ◯ Pub/Sub Emulator
 ◯ Storage Emulator
(Move up and down to reveal more choices)

ポート： 9000
emulator download Y

? Which Firebase emulators do you want to set up? Press Space to select 
emulators, then Enter to confirm your choices. Database Emulator
i  Port for database already configured: 9000
i  Emulator UI already enabled with port: (automatic)
? Would you like to download the emulators now? Yes
i  ui: downloading ui-v1.11.4.zip...

i  Writing configuration info to firebase.json...
i  Writing project information to .firebaserc...

✔  Firebase initialization complete!

作成されたfirebase.json

{
  "emulators": {
    "database": {
      "port": 9000
    },
    "ui": {
      "enabled": true
    },
    "singleProjectMode": true
  }
}

エミュレーター起動

$ firebase emulators:start

i  emulators: Starting emulators: database
⚠  database: Did not find a Realtime Database rules file specified in a firebase.json config file. The emulator will default to allowing all reads and writes. Learn more about this option: https://firebase.google.com/docs/emulator-suite/install_and_configure#security_rules_configuration.
i  database: Database Emulator logging to database-debug.log
⚠  emulators: The Emulator UI is not starting, either because none of the emulated products have an interaction layer in Emulator UI or it cannot determine the Project ID. Pass the --project flag to specify a project.

┌─────────────────────────────────────────────────────────────┐
│ ✔  All emulators ready! It is now safe to connect your app. │
└─────────────────────────────────────────────────────────────┘

┌──────────┬────────────────┐
│ Emulator │ Host:Port      │
├──────────┼────────────────┤
│ Database │ 127.0.0.1:9000 │
└──────────┴────────────────┘
  Emulator Hub not running.
  Other reserved ports: 4500

Issues? Report them at https://github.com/firebase/firebase-tools/issues and attach the *-debug.log files.

[警告]カレントのプロジェクトが指定されていない旨の警告

⚠  emulators: The Emulator UI is not starting, either because none of the emulated products have an interaction layer in Emulator UI or it cannot determine the Project ID. Pass the --project flag to specify a project.

↓

プロジェクト設定
$ firebase use [Project ID]

Now using project [Project ID]

カレントプロジェクト設定後
- http://127.0.0.1:4000/ にてエミュレーターにアクセス可能に

i  emulators: Starting emulators: database
⚠  database: Did not find a Realtime Database rules file specified in a firebase.json config file. The emulator will default to allowing all reads and writes. Learn more about this option: https://firebase.google.com/docs/emulator-suite/install_and_configure#security_rules_configuration.
i  database: Database Emulator logging to database-debug.log
i  ui: downloading ui-v1.11.4.zip...
Progress: ========================================================================================> (100% of 4MB)
i  ui: Emulator UI logging to ui-debug.log

┌─────────────────────────────────────────────────────────────┐
│ ✔  All emulators ready! It is now safe to connect your app. │
│ i  View Emulator UI at http://127.0.0.1:4000/               │
└─────────────────────────────────────────────────────────────┘

┌──────────┬────────────────┬────────────────────────────────┐
│ Emulator │ Host:Port      │ View in Emulator UI            │
├──────────┼────────────────┼────────────────────────────────┤
│ Database │ 127.0.0.1:9000 │ http://127.0.0.1:4000/database │
└──────────┴────────────────┴────────────────────────────────┘
  Emulator Hub running at 127.0.0.1:4400
  Other reserved ports: 4500

Issues? Report them at https://github.com/firebase/firebase-tools/issues and attach the *-debug.log files.

エミュレーターUI
エミュレーターの RealtimeDatabase 操作
- connectDatabaseEmulator で接続先を Emulator に

firebase.tsx

import { initializeApp } from "firebase/app";

const firebaseConfig = {
  apiKey: process.env.REACT_APP_apiKey,
  authDomain: process.env.REACT_APP_authDomain,
  projectId: process.env.REACT_APP_projectId,
  storageBucket: process.env.REACT_APP_storageBucket,
  messagingSenderId: process.env.REACT_APP_messagingSenderId,
  appId: process.env.REACT_APP_appId,
  databaseURL: process.env.REACT_APP_database,
};

const app = initializeApp(firebaseConfig);
export const db = getDatabase(app);

if (process.env.NODE_ENV !== "production") {
  // エミュレーターに接続する
  connectDatabaseEmulator(db, "localhost", 9000);
}

書き込みできた！