function parseQuantity(args) {
  if (args.length !== 1 || !/^[1-9][0-9]*$/.test(args[0]))
    throw new Error('Use one positive quantity');
  const value = Number(args[0]);
  if (!Number.isSafeInteger(value) || value > 20)
    throw new Error('Quantity out of range');
  return value;
}
console.log(parseQuantity(['3']));
try {
  parseQuantity(['3kits']);
} catch (error) {
  console.log(error.message);
}