Support custom validators for non-required fields

[kevinoid]

The fact that errors for non-required fields are ignored can really limit the utility of custom validators. It would be great if express-form could either integrate some mechanism for custom validators on non-required fields or non-field-specific/multi-field validation.

The particular use case that I have in mind is to be able to check for conditionally required fields. For example, field2 is required if field1 is provided (or if field1 has a particular value). I didn't see a way to implement this sort of logic in the current design and it would be very useful for me at the moment.

Thanks for considering,
Kevin

[nanoamp]

It's probably a bit late now, but there's a response to another issue - #2 - which provides a possible solution by using something like

form.field('field2').custom(function(value, source) {
  if (source.field1 != undefined ) {
    // do stuff
  }
  ...
}

[kevinoid]

Unfortunately, that solution only works if field2 has a value. Otherwise any error returned from the // do stuff block would be ignored.

The issue here is that custom validation is ignored when non-required fields don't have a value. I only brought up the conditional-dependency as a motivating example for why such functionality could be useful. Sorry if that was confusing.

[nanoamp]

Ah, now I see what you mean. You're welcome to try the fork I've been working on today, to which I've added a .validateCustomIfEmpty() method. I'll probably pull-request it to here when our changes are stable.