실시간 데이터베이스 개요
https://firebase.google.com/docs/database/?hl=ko
웹용 실시간베이스
https://firebase.google.com/docs/database/web/start?hl=ko
웹용 데이터베이스 읽고 쓰기
https://firebase.google.com/docs/database/web/read-and-write?hl=ko
웹용 clodelab
https://codelabs.developers.google.com/codelabs/firebase-web/?hl=ko#0
Github 예제
https://github.com/firebase/quickstart-js/tree/master/database
