Memoization with Fibonacci

memoized-fibonacci.js

// find fibonacci number at n index
const fibonacci = (n) => {
  // fibonacci at 0 index and at 1 index is always 1
  if (n <= 1) {
    return 1;
  }

  // 2 index and later value will be the the sum of the 2 numbers before the index;
  return fibonacci(n - 1) + fibonacci(n - 2); 
}

// memoization for all functions
const memoizer = (fn) => {
  // create cahe
  const cache = {};

  // return function that have access to the cache
  return (n) => {
    // check if value exist in cache
    if (cache[n] != undefined) {
      return cache[n];
    }

    // if it doesn't exist, calculate the result
    cache[n] = fn(n);
    return cache[n];
  }
}

// combine fibonacci with memoizer, else it will not retain the cache
const memoizedFibonacci = memoizer(fibonacci);

// TEST ELAPSED TIME
const testRepetition = 1000; // test repetition to do
const atIndex = 25; // fibonacci index to find

// WITHOUT MEMOIZATION
// each fibonacci call with the same parameter will be calculated
console.time('without memoization');
for (let i = 0; i < testRepetition; i++) {
  fibonacci(atIndex);
}
console.timeEnd('without memoization');

// WITH MEMOIZATION
// only the first fibonacci call with the same parameter will be calculated
// second and later call with the same parameter will be taken from cache
console.time('with memoization');
for (let i = 0; i < testRepetition; i++) {
  memoizedFibonacci(atIndex);
}
console.timeEnd('with memoization');