how to create an offline web app using javascript

I am looking for a solution on how to create an offline compatible web app using html, JavaScript, and maybe jQuery. I looked into service workers, but they aren’t comparable with all mobile devices yet. I also looked at the manifest file thing, it worked but it didn’t update the files. So now I’m here asking for a solution. I intend this application to be a music website that can be a web app. I like music and i take it everywhere so I’m trying to find out how i can save the website files for offline use so even if I don’t have WiFi, i can listen to my saved music. btw the files I’d like to save are:

main.js
Main.css
Index.html