Use service workers

[TrueDoctor]

https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API
Thanks to @AsyncTheory for bringing this to my attention

1. You can load the page, close it, turn off your internet and open that link again, it should load even when you're offline
2. If you open the page on a mobile browser, add it to your home screen using a button in your browser and launch it from the home screen, the page will open without the browser UI like a real native app