findPrimeFactors.ts

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

const numbers = [99999, 12, 15];
const allFactors = [];

for (let num of numbers) {
  for (let i = 1; i <= num; i++) {
    if (num % i === 0) allFactors.push(num);
  }
}

const allPrimeFactors = allFactors.filter(isPrime);
console.log(allPrimeFactors);