Tcomb-form-native: Conditional Validation Error Messages

[jonlong]

Big thanks for this library!

I've got a use case where I want to validate a form field, but provide a different error message based on the criteria that fails.

For example, say I have a "Name" field that needs all of the following to validate:

• Max Length
• No Emojis
• Isn't Blank

And for each of those cases, I'd like to provide a specific error message:

• "The maximum character length is 20"
• "Sorry, we don't support emojis yet!"
• "We need a name to proceed!"

My understanding is that I'd use a refinement to add the custom validation logic, but I'm struggling to figure out how to create conditional messages based on the criteria that fails. Ideally if more than one fails, I could return multiple messages.

Can anyone point me in the right direction? Would be happy to add an example to the repo once I've got it figured out!

[gcanti]

In your use case I think that the easiest way would be to define a getValidationErrorMessage function (https://github.com/gcanti/tcomb-form-native#error-messages)

// predicates
var max20 = s => s.length <= 20;
var noemojis = s => s.indexOf('👦') === -1;

var Name = t.refinement(t.String, s => max20(s) && noemojis(s));

Name.getValidationErrorMessage = s => {
  if (!s) {
    return 'We need a name to proceed!';
  }
  if (!max20(s)) {
    return 'The maximum character length is 20';
  }
  if (!noemojis(s)) {
    return 'Sorry, we don\'t support emojis yet!';
  }
};

var FormType = t.struct({
  name: Name
});

[jonlong]

@gcanti Perfect, thank you!