Code split into multiple functions

user.code_split.service.js

/**
 * This method will verify user credentials and return adequate response
 * @param userName username or email of user
 * @param password password of the user
 */
function login(userName, password) {
  /*
   * Validate user credentials, moved to separate function
   */
  validateCredentials(userName, password);
  /*
   * DB Operation: Query the user by his credentials
   */
  const user = UserSchema.find({ email: userName, password: password });

  /*
   * Validation: user not found, invalid credentials
   */
  if (!user) {
    throw new Error(`Invalid credentials`);
  }

  /*
   * Validate user status, moved to separate function
   */
  return validateStatus(user);
}

/**
 * This method will validate username & password
 * @param userName username or email of user
 * @param password password of the user
 */
function validateCredentials(userName, password) {
  /*
   * Validation: Check if username is not supplied
   */
  if (!userName) {
    throw new Error(`No username`);
  }

  /*
   * Validation: Check if password is not supplied
   */
  if (!password) {
    throw new Error(`No password`);
  }
}

/**
 * This method will validate user's status
 * @param user user data
 */
function validateStatus(user) {
  let response = {};

  /*
   * User status check: return response as per user status
   */
  switch (user.status) {
    //////////////////////////////
    //          Active          //
    //////////////////////////////
    case "Active":
      response = { message: "Login successful", user: user };
      break;

    //////////////////////////////
    //          Inactive        //
    //////////////////////////////
    case "Inactive":
      response = { message: "User is inactive", user: undefined };
      break;

    //////////////////////////////
    //          Invited         //
    //////////////////////////////
    case "Invited":
      response = { message: "User is not activated yet", user: undefined };
      break;

    //////////////////////////////
    //          Blocked         //
    //////////////////////////////
    case "Blocked":
      response = { message: "User is blocked", user: undefined };
      break;

    //////////////////////////////
    //    Invalid Status        //
    //////////////////////////////
    default:
      response = { message: "User with invalid status", user: undefined };
      break;
  }

  /*
   * Return response
   */
  return response;
}