Mini MVCS Errors

Small Utility library for handling and transforming errors in a rest app style, but it could be used in any other setting.

Extracted first from Mini MVCS Library and from Node Backend Skel for individual use without any other dependencies.

Features

• Throw Errors that follow a simple convention whenever you want
• Transform Errors to keep flow of the application

Installation

Using npm:

npm install --save mini-mvcs-errors

Usage

This library provides one main Error Abstract Class (but extensible) and two other frequently used error classes

ApiError

The base class which other classes extend from

NotFoundError

The error to use when searching for a resource and it is not found

constructor params

• resourceName (String): Name of the resource
• filter (Object): Filters used to find the resource

Example:

const searchBookWrapper = (bookId) => {
  return methodForSearchingBook(bookId)
  .then((result) => {
    // the method returns null when a resource is not found
    if (!result) {
      throw new NotFoundError('Book', { id: bookId });
    }
    return result
  });
};

ValidationError

The error to use when executing an operation that could not be completed because the user made an error

constructor params

• resourceName (String): Name of the resource or executing operation
• fieldErrors (Array): A list of the errors that the user made

Example:

const createBookWrapper = (book) => {
  if (!book.name) {
    throw new ValidationError('Book', [
      new FieldError('name', 'null'),
    ]);
  }
  return methodForCreatingBook(book)
};

FieldError

Although not a proper Error (can not be throwed) it is used for having a unique format for the body of the ValidationError

Transforming

Both AuthorizationError and NotFoundError provide an static method that allows them to be catched and transformed to some successful result or another error

Example:

// the creation of the Book should only return if a book is created successfully or throw a ValidationError if something is wrong (e.g.: the author relationship is not found)
const createBookWrapper = (book) => {
  return database.searchAuthorById(book.authorId)
  // it throws a NotFoundError when the authorId does not exists in the database
  .catch(NotFoundError.handle((notFoundErrorInstance) => {
    // the notFoundErrorInstance is provided for using in our code
    // we handle the NotFoundError by throwing a ValidationError
    throw new ValidationError('Book', [
      new FieldError('author', 'invalid', [book.authorId]);
    ]);
  }))
  // the author exists
  .then(() => {
    return database.createBook(book)
  });
};

the NotFoundError.handle is a shortcut for:

.catch((error) => {
  if (error instanceof NotFoundError) {
    // ... callback
    return callbackPassedInHandle();
  }
  throw error;
});

Sometimes you just want to return a simple value to the callback of the .handle method, in that case you just need to pass it as the only param

Example:

const createBookWrapper = (book) => {
  return database.searchAuthorById(book.authorId)
  // it throws a NotFoundError when the authorId does not exists in the database
  .catch(NotFoundError.handle({ id: 1 })) // default author to be used
  // using the sent author if found or the default author
  .then((author) => {
    // modifying the book to be created
    return database.createBook({
      ...book,
      authorId: author.id,
    })
  });
};

There are some other common uses for the .handle method that I will put here in the future

License

MIT