haskell_listToMaybe.js

// const :: a -> b -> a
const Const = a => _ => a

// Just :: a -> Maybe a
const Just = a => ({ _tag: 'Just', a });

// Nothing :: Maybe a
const Nothing = { _tag: 'Nothing' };

// (.) :: (b -> c) -> (a -> b) -> a -> c
const compose = bc => ab => a => bc(ab(a));

// foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b
const foldr = abb => b => ta => ta.reduceRight((b, a) => abb(a)(b), b);

// listToMaybe :: [a] -> Maybe a
// listToMaybe = foldr (const . Just) Nothing
const listToMaybe = foldr(compose(Const)(Just))(Nothing);

console.log( listToMaybe(['first', 'second', 'third']) ); // { _tag: 'Just', a: 2 }
console.log( listToMaybe([]) ); // { _tag: 'Nothing' }