i've always wondered how web and functional programming interact. there's, for example TypeScript and Elm. These are not designed for mathematical proofs.
http://www.impredicative.com/ur/
https://wiki.haskell.org/Web/Frameworks
Note: You'd pick the purest of them probably.
Most work I've seen on web applications with formal focus used model checkers, though.
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.397....