Cloud Functions から Firebase Cloud Messaging を呼び出す最小構成

functions_index.js

import * as functions from 'firebase-functions'
import * as admin from 'firebase-admin'

admin.initializeApp({
  credential: admin.credential.applicationDefault(),
  // databaseURL: 'https://hoge.firebaseio.com/',
})

export const api = functions.https.onRequest(async (req, res) => {
  const message = {
    topic: 'TOPIC_NAME',
    notification: {
      title: '通知デモです',
      body: `サーバーは${new Date().getHours()}時です。`,
    },
    // priority: 'high',
  }
  admin.messaging().send(message)
})