Mongodb realm with my own backend

Hi team,
As I understood that mongodb realm work as backend as a service, but I want to use my own backend as express js and frontend with react or any other and want to use realm as local database + mongodb as online database, can I use like this, if yes then how?
Like how whatsapp store our chat offline on our device and sync with online database while online.

Hi @Nayan_Rathod - yes, you can use the Realm JS SDK with express js as a backend service to serve up your react pages. The data will be stored in a local Realm database file in your backend that will synchronize with Atlas (and your MongoDB database) in the cloud.
Here is an example for getting started with express js and Realm: Building a Blog with Realm Node.js and Express

Sorry, that example I gave is fairly outdated (from 2017) - here is a more recent example/tutorial:
Here is the MERN Stack Crash Course tutorial referenced in the video:
Hopefully this helps you to get started.