better readable fn than listed here https://folktale.origamitower.com/api/v2.3.0/en/folktale.result.html

validateBranching-folktale.js

const validateBranching = ({ name, type, email, phone }) => {
  if (!isValidName(name)) 
    return Required('name');
  
  if (type === 'email') {
    if (!isValidEmail(email)) 
      return InvalidEmail(email);
    if (phone && !isValidPhone(phone)) 
      return Optional(InvalidPhone(phone));
    return { type, name, email, phone };
  } 
  
  if (type === 'phone') {
    if (!isValidPhone(phone)) 
      return InvalidPhone(phone);
    if (email && !isValidEmail(email)) 
      return Optional(InvalidEmail(email));
    return { type, name, email, phone };
  }
  
  return InvalidType(type);
};