Typescript function to check if a given value is a valid port number

is-valid-port-number.ts

const isPortnumber = (value: number): boolean => {
  // https://en.wikipedia.org/wiki/Registered_port
  return value >= 0 && value <= 65535;
};
                                     
const isValidPortnumber = (value: unknown): value is number => {
  if (typeof value === "number") {
    return isPortnumber(value);
  }

  if (typeof value === "string") {
    return isPortnumber(Number(value));
  }

  return false;
};