memoize.js

/*
This memoize function takes in another function as its argument (func) 
and returns a new function that caches the results of func based on its arguments.

The returned function first checks if the arguments have already been cached 
by checking if there is a key in the cache object with the same JSON stringified arguments (key). 
If there is a cached value, it returns it. If not, it invokes the original function func with the arguments, 
caches the result under the key, and returns the result.
*/

function memoize(func) {
  const cache = {};
  
  return function(...args) {
    const key = JSON.stringify(args);
    
    if (cache[key]) {
      return cache[key];
    } else {
      const result = func.apply(this, args);
      cache[key] = result;
      return result;
    }
  }
}

// You can use this memoize function like this:

function expensiveCalculation(n) {
  console.log(`Calculating for ${n}...`);
  return n * n;
}

const memoizedCalculation = memoize(expensiveCalculation);

console.log(memoizedCalculation(2)); // "Calculating for 2..." then 4
console.log(memoizedCalculation(2)); // 4 (retrieved from cache)
console.log(memoizedCalculation(3)); // "Calculating for 3..." then 9
console.log(memoizedCalculation(3)); // 9 (retrieved from cache)