UserModel.ts

interface CreateUserRequest {
  username: string;
  age: number;
  email: string;
}

interface UpdateUserRequest {
  username?: string;
  age?: number;
  email?: string;
}

const createUser = (user: CreateUserRequest) => {
  //fetch request that requires all User properties
}

const updateUser = (user: UpdateUserRequest) => {
  //fetch request that doesn't require any User properties
}