Comment by tylerchurch

I always interpret “core” as “no libraries”. What can you do with just your browser and an HTML file?

Poke through MDN and see what you find.

Do you know about dialog? https://developer.mozilla.org/en-US/docs/Web/HTML/Element/di...

MutationObserver? https://developer.mozilla.org/en-US/docs/Web/API/MutationObs...

URL? https://developer.mozilla.org/en-US/docs/Web/API/URL_API