js-dos supports saving and restoring game progress. You can play game from time to time without losing progress. It's working automatically while you don't change bundle url.
This feature works by dumping changes of file system into second
bundle and use it to override original file system
on next load. This feature is backed by CommandInterface
You can implement your own save/load feature like this:
While you use default Save/Load feature of js-dos all updates are stored in indexed db
The changes bundle is stored like key value record, where key is a
bundle url and value is
All progress will be lost if you change bundle url.