There's a good article about this written by the founder of the site here: dev.to/ben/what-it-takes-to-render...
They're also now making use of Service Workers for caching, I think: dev.to/ben/what-the-heck-is-a-prog...
One of the (many) reasons why I like this site is how open they are about its development :)
Well I find the more you share the more you learn through feedback or the learning you have to do in order to share intelligibly. The more we can help others, the better. You're correct on the service worker stuff, although our implementation isn't taking advantage of everything. It's definitely an API I'm interested in leveraging more and more of.
Our codebase is a fairly conventional Rails app with some design constraints in order to make things as cacheable as possible and a few tricks on the client to try and prefetch resources where possible. It's always a work in progress and I hope we can keep getting faster and more reliable through greater understanding of service workers and more commitment to the fundamentals of latency reduction.
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