largestPrimeFactor.js

function largestPrimeFactor(num) {
  let larFac = 0;
  let count = 2;
  while (count * count <= num) {
    if (num % count === 0) {
      num /= count;
      larFac = count;
    } else count++;
  }
  if (num > larFac) larFac = num;
  return larFac;
}

console.log(largestPrimeFactor(13195)); // 29