1. const memoize = fn => new Proxy(fn, {
    2.   cache: new Map(),
    3.   apply (target, thisArg, argsList) {
    4.     let cacheKey = argsList.toString();
    5.     if(!this.cache.has(cacheKey))
    6.       this.cache.set(cacheKey, target.apply(thisArg, argsList));
    7.     return this.cache.get(cacheKey);
    8.   }
    9. });
    11. const fibonacci = n => (n <= 1 ? 1 : fibonacci(n - 1) + fibonacci(n - 2));
    12. const memoizedFibonacci = memoize(fibonacci);
    14. for (let i = 0; i < 100; i ++)
    15.   fibonacci(30);                      // ~5000ms
    16. for (let i = 0; i < 100; i ++)
    17.   memoizedFibonacci(30);              // ~50ms