Roughly simulate the difference between pointfree style and pointful style. Inspired by https://kakkun61.hatenablog.com/entry/2019/07/29/%E9%96%A2%E6%95%B0%E3%81%AE%E3%83%A1%E3%83%A2%E5%8C%96

fact.js

/*
fact :: Int -> Integer
fact 0 = 1
fact n = fromIntegral n * fact (n-1)
*/
const fact = function(n){
  if (n == 0){
    return 1;
  } else {
    return n * fact(n - 1);
  }
};

/*
fact3 :: Int -> Integer
fact3 = (map fact [0..] !!)
  where
    fact 0 = 1
    fact n = fromIntegral n * fact (n-1)
*/
const fact3 = function(){
  // Up to 1000 because infinite list is hard to express in JavaScript
  const facts3 = [...Array(1000).keys()].map((n) => fact(n));
  return function(n){
    return fact3[n];
  };
};

/*
fact4 :: Int -> Integer
fact4 x = map fact' [0..] !! x
  where
    fact' 0 = 1
    fact' n = fromIntegral n * fact' (n-1)
*/
const fact4 = function(){
  return function(n){
    // Up to 1000 because infinite list is hard to express in JavaScript
    const facts4 = [...Array(1000).keys()].map((n) => fact(n));
    return fact4[n];
  };
};

Unfortunately, I failed to compare the performance difference between fact3 and fact4.
Because JavaScript's Number gets overflown easily (I should rewrite with BigInt, but cumbersome!), and JavaScript's stack size is too small.