What is the Application Cache in HTML5 and why it is used?

Answer 1

https://www.html5rocks.com/en/tutorials/appcache/beginner/

Answer 2

https://developer.mozilla.org/en-US/docs/Web/API/Window/applicationCache
https://medium.com/@firt/service-workers-replacing-appcache-a-sledgehammer-to-crack-a-nut-5db6f473cc9b