Promise should reject with Error object

[Andreyco]

Current behaviour: When validation fails, Promise is rejected with array object.

Expected behaviour Instead, it should be rejected with Error object. Node happen to complain about this.

Notes Rejecting with Error object would probably cause breaking change.

[thetutlage]

There is a difference between an error and an exception. The error object is created when an exception is thrown and developers are tend to deal with them.

Whereas validation falls in errors category, where you need a sensible object/array with custom messages, so that you can let people understand and act upon them.

The Promise spec may says that rejection should have error object, but specs are not written keeping business logic in mind.

[Andreyco]

I totally agree with you... What I was talking about is something like this...

Custom validation error object

function ValidationError(errors) {
  this.name = 'ValidationError';
  this.message = 'fix you things';
  this.stack = (new Error()).stack;

  this.errors = errors;

  this.getAll = function() {
    // return all
  }

  this.getForKey = function(key) {
    // return all errors for given key
  }

  this.getFirstForKey = function(key) {
    // return first error for given key
  }
}

ValidationError.prototype = Object.create(Error.prototype);
ValidationError.prototype.constructor = ValidationError;

Validation fn

function validate(data, schema, messaged) {
  return new Promise((resolve, reject) => {
    if (fails) {
      reject(new ValidationError(errArray));
    }

    resolve(true || orWhatever)
  });
}

Handle validation

try {
  await validate(data, rules, messages);
} catch (valErr) {
  console.log(valErr.getAll());
}

Pros

• satisfies Promise rejection by providing instance of Error as rejection reason. Node won't complain anymore (not sure whether browser does complain at all)
• easily allows things like getAll, getAllFor, getFirstFor, ... without bloating validator itself (yep, could be added via helper functions)

Cons

• introduces little overhead.

[thetutlage]

Ideally yes, but I am planning to add support for error formats, where you can define a format in which errors should be received.

Not sure if it will be possible to always reject with an error, since it will be dependent upon the formatted your are using.

[ansarizafar]

I totally agree with @Andreyco. Is the suggested change merged. Can I handle validation like this now.

try {
  await validate(data, rules, messages);
} catch (valErr) {
  console.log(valErr.message);
}