example.ts

class ErrorBase<T> extends Error {
  constructor(public readonly type: string, public readonly reason: string) {
    super(reason)
  }
}

class MemberCreateInputError extends ErrorBase<MemberCreateInputError> {
  constructor(reason: string) {
    super('invalid.member_create_input', reason)
  }
}

class MemberEmailAlreadyInUseError extends ErrorBase<MemberEmailAlreadyInUseError> {
  constructor(reason: string) {
    super('invalid.member_email_already_in_use', reason)
  }
}

class MemberPhoneAlreadyInUseError extends ErrorBase<MemberPhoneAlreadyInUseError> {
  constructor(reason: string) {
    super('invalid.member_phone_already_in_use', reason)
  }
}

type MemberCreateError =
  | ErrorBase<MemberCreateInputError>
  | ErrorBase<MemberEmailAlreadyInUseError>
  | ErrorBase<MemberPhoneAlreadyInUseError>

class MemberCreateUseCase {
  handle(input: MemberCreateInput): Either<MemberCreateError, MemberFullOutput> {
    ...
  }
}
  
  
class MemberCreateController {
  handle() {
    const result = this.useCase.handle(...)

    if (result.isLeft()) {
      if (result.getValue() instanceof BaseError) {
        return new Response('Bad Request')
      }
      
      return new Response('Server Error')
    }
    
    return Response(result.getValue())
  }
}