Where is the applicative in my Javascript traverse implementation?

Question

I've tried to understand Haskell's traverse function and to implement it in Javascript, but I'm stuck. When I look at its type (Functor t, Foldable t, Applicative f) => (a -> f b) -> t a -> f (t b), I understandd that I need <$> (map in JS), <*> (ap in JS) and fold in order to implement it.

I came up with the following code:

// Church encoded Identity newtype

const Ident = x => f => f(x);

const traverse = map => ft => tx => map(y => Ident(y)) (tx(x => ft(x)));

// list functor

map = f => xs => xs.map(f);

// helper

I = x => x;

// data

idA = Ident(1);
idB = Ident(null);

// and run

const r1 = traverse(map) (x => x === null ? [] : [x]) (idA); // [Ident(1)]
const r2 = traverse(map) (x => x === null ? [] : [x]) (idB); // []

console.log(r1 [0] (I)); // 1
console.log(r2); // []

Since I used Ident and Array the type simplifies to (a -> [b]) -> Ident a -> [Ident b]. traverse runs the effect when it rebuilds the data structure. If I am not mistaken one can observe the non-deterministic effect of the list functor in my example.

But where is the applicative? And why does the traversable have to be a functor? Is it just a coincidence that I didn't need them for my sketch?