I have to create HTML5 application that downloads content when you have internet connection. After that you can loose connection and keep working on it. When connection is available agian it should synchornise all data with server. It should persist data over restarting program/browser. I think Slack and Visual Studio Code are written in this way.
According to my research I have to use the Manifest file to download recourses and use File API
For now I found that Chrome devTools are best for this purpose.
Have you other ideas how can I create such application? The important thing is it should be cross-platform.