js计算1000以内的质数

function isPrime(num) {
  if (num <= 1) return false;
  for (let i = 2; i * i <= num; i++) {
    if (num % i === 0) return false;
  }
  return true;
}

function getPrimesUnderLimit(limit) {
  const primes = [];
  for (let i = 2; i < limit; i++) {
    if (isPrime(i)) {
      primes.push(i);
    }
  }
  return primes;
}

const primesUnder1000 = getPrimesUnderLimit(1000);
console.log(primesUnder1000);

function sieveOfEratosthenes(limit) {
  const isPrime = new Array(limit).fill(true);
  isPrime[0] = isPrime[1] = false;
  for (let i = 2; i * i < limit; i++) {
    if (isPrime[i]) {
      for (let j = i * i; j < limit; j += i) {
        isPrime[j] = false;
      }
    }
  }
  return isPrime.map((prime, index) => prime ? index : null).filter(Boolean);
}

const primesUnder1000 = sieveOfEratosthenes(1000);
console.log(primesUnder1000);