primes_map.js

function isPrime(num) {
  for (let i = 2, s = Math.sqrt(num); i <= s; i++)
    if (num % i === 0) return false;
  return num > 1;
}

function getMapOfPrimeNumbersUpTo(n) {
  const result = new Map();
  for (let i = 0; i < n; i++) {
    if (isPrime(i)) result.set(i, true);
  }
  return result;
}

const primesMap = getMapOfPrimeNumbersUpTo(300);
console.log(primesMap.has(71), primesMap.has(72));