check: support default options for validationResult

[alrav]

This is a proposal to resolve #427, by introducing a way to set default options for the validation-result module

It introduces a new .withDefaults function, which will return a new instance of the module with specified default options. The decision to return a new instance was to avoid affecting the global module state in the case that multiple validationResult implementations are desired within the same application.

This is loosely inspired on the concept of request.defaults from the request/request module

Here's a brief example:

// baseValidationResult.js ----
const { validationResult } = require('express-validator/check');

const result = validationResult.withDefaults({
    formatter: (error) => {
        return {
            myLocation: error.location,
        };
    }
});

module.exports = result;

// within an express router ----
const validationResult = require('./baseValidationResult');

errors = validationResult(req);

if (!errors.isEmpty()) {
  return res.status(422).json({
    errors: errors.mapped(),
  });
}

Note: This is my first time getting acquainted with TypeScript, so let me know if the definitions make sense

[coveralls]

Coverage remained the same at 100.0% when pulling 68c949f on alrav:issue-427-validation-result-defaults into ead6b75 on ctavan:master.

[gustavohenke]

This is perfect - thanks!!
Exactly how I would approach that issue.

I left some comments regarding minor things though.
Can you please fix them?

[gustavohenke]

Saying "a new validation result instance" could be misleading.
What do you think of rewriting it to say that a new validationResult function is returned, using the provided options? Will also be great to link to that function's section in the docs!

[alrav]

Makes perfect sense to me

[gustavohenke]

Can you use validationResult.withDefaults()? So that it matches the documented example.
I think this will also require changes to how the type declaration is done...

[gustavohenke]

It will also be worth changing the test to const result: ValidationResult = validationResult.withDefaults(...)(req).
Should catch all possible typing bugs...

[alrav]

I think it should be set now.

I kept validationResult interface as lower-camel-cased, since it might be more easily identifiable as a function. If any objections, I can also change to ValidationResult.

[alrav]

Thanks for the feedback and absolutely! I'm working on addressing your requested changes 👍

[coveralls]

Coverage remained the same at 100.0% when pulling de770e2 on alrav:issue-427-validation-result-defaults into ead6b75 on ctavan:master.

[alrav]

Hello @gustavohenke - comments addressed. Let me know if anything else needs a tweak.

[coveralls]

Coverage remained the same at 100.0% when pulling 8c6245e on alrav:issue-427-validation-result-defaults into ead6b75 on ctavan:master.

[gustavohenke]

Thanks again!

[lock]

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