I'm having trouble grokking whatever type-added syntax you're using for Javascript here. I'm guessing it's:

  function ap(pf) {
    return (pa) =>
      pf.then((f) => pa.then((a) => Promise.resolve(f(a))))
  }

Still, if I wanted to go full-hog static-typed functional I doubt I'd be using straight Javascript, I'd probably try one of the various Haskell-alike to JS converters. Promises with async/await syntax seems like the most practical of the various solutions whilst still feeling like Javascript.

(Besides, I prefer dynamic typing and I find points-free style in Haskell to be obfuscating rather than clarifying, so it seems unlikely we're going to have the same opinion of the best way to accomplish things here. :)