SImpleMemoize.js

// Check if given number is prime
const isPrime = number => {

  if (number < 2) return false;
  
  // Divide number by all numbers from 2 to sqrt(number)
  // If divisible, then its not a prime
  let div;
  for (div = 2; div < Math.sqrt(number); div++)
    if (number % div == 0) {
      console.log(`Looped ${div} times`);
      return false;
    }
  console.log(`Looped ${div} times`);
  return true;
}

const memoize = fn => {
  // We store previous results here
  const cache = {};

  // Return a function to be called
  return memoized = (...args) => {

    // If result not in cache, first cache it
    if (!(args in cache))
      cache[args] = fn(...args);
    
    // Now return it
    return cache[args];
  }
}

// This is a known prime
let number = 1299827;
const smartPrime = memoize(isPrime);
console.log(`${number} is prime: ${smartPrime(number)}`);
console.log(`${number} is prime: ${smartPrime(number)}`);

/* Output
Looped 1141 times
1299827 is prime: true
1299827 is prime: true
*/