memo-example.js

// const freezeFn = fn => (c => x => c[x] != null ? c[x] : c[x] = fn(x))({})
const freezeFn = fn => (c => {return function cached(x){if (c[x] != null) {c[x] = fn(x, cached)}; return c[x]}})({})

const fibFn   = (x, fn) => fn(x - 1) +  fn(x - 2)
const fibArgs = (x, fn) => +!parseInt(x) || +(x == 0) || +(x == 1) || fibFn(parseInt(x), fn)
const fibonacci = freezeFn(fibArgs)

const facFn   = (x, fn) => x * fn(x - 1)
const facArgs = (x, fn) => +!parseInt(x) || +(x == 0) || +(x == 1) || facFn(parseInt(x), fn)
const factorial = freezeFn(facArgs)