Example memoize implementations

memoize.js

/** Memoize takes a function as an argument and returns a function. When the supplied function is called, it is stored in a 
*   lookup table. That way the next time it's called the passed function won't run again and will instead return the stored value. 
*/
function memoize (fn) {
  var cache {}
  return function () {
    var args = Array.prototype.slice.call(arguments)
    var key = JSON.stringify(args)
    if (key in cache) return cache[key]
    else {
      return cache[key] = fn.apply(this, args)
    } 
  }
}

// ES6 implementation with rest operator
const memoize = (fn) => {
  let cache = {}
  return function (...args) {
    let stored = JSON.stringify(args)
    return cache[stored] || (cache[stored] = fn.apply(this, args))
}

// example
const fibMem = memoize((n) => n < 2 ? 1 : fibMem(n - 2) + fibMem(n - 1))
fibMem(100) // => 573147844013817200000