I don't mind sharing my code through REPLIT.
But I would like to keep the data I'm using secret. Is there anyway to keep JSON file secret (like .env, it's not shared, even though the repl is shared) ?
Storing data in repl.it is not recommended because when you edit data stored in files on repl.it programmatically, you will love all the changes very soon. So I recommend using some external database. If you want to stick to JSON, then you can use any service similar to jsonstore.io. In case you're using python or Nodejs, there are some packages that you can use to use jsonstore API in an easy way.
Please mark this as the correct answer if it helps.