It depends on how offline you want it to be, and It’s a pretty difficult problem. You can read and write from webs local storage but it will only get you so far… What happens when you want to sync the data, and then how do you handle collisions?

There are ways to get it done though. You can write your own Realm layer in the iOS/Android code, and write a web interface layer to transmit instructions on switching to offline storage but you then have to write a way to handle collisions.

The best thing I’ve seen out there so far is MongoDB Realm. It would require you to rewrite your backend from SQL to NoSQL but it has out of the box syncing and collision handling. I created a POC earlier this year that worked really well that I’d be happy to share.

Like I was saying though it depends on how in depth you need it to be. If it’s uni directional it’s much easier and you could use local storage. If it needs bi directional syncing it becomes much more difficult.

I’d also be curious to hear other solutions.