Customizing global error messages

[ChrisGambrell]

I love express-validator, but the one thing I miss from Joi is global error messages. In Joi, I could do something like...

const errorMessages = {
    'any.required': 'The field "{#key}" is required.',
    'string.base': 'The field "{#key}" needs to be a string.',
    'string.empty': 'The field "{#key}" cannot be empty.'
}

const schema = Joi.object({
    name: Joi.string().trim().required(),
    dob: Joi.string().optional()
})

const { ... } = schema.messages(errorMessages).validate({ ... })

... and get nice error messages that I could handle globally. When I create my schemas in express-validator and want to use isString(), I have a custom error message for this ValidationChain, but I have to chain the .withMessage({ ... }) with every instance of isString() to use my custom message.

Is there a way to achieve this behavior with express-validator that I am just not aware of/familiar with? Thanks so much in advance.

[ChrisGambrell]

Another option I had thought of was creating my own ValidationChain and using it repeatedly everywhere with the message included, but I wasn't sure how to do that. Something like....

app.post('/foobar', body('foo').isCustomString(), (req: Request, res: Response) => { ... })

Where .isCustomString() is really .isString().withMessage('some dynamic message')

[ChrisGambrell]

My temporary fix feels ugly and dirty but is as follows...

const exists = (before: ValidationChain): ValidationChain => before.exists().withMessage('This is required').bail()
const isString = (before: ValidationChain): ValidationChain => before.isString().withMessage('Must be a string').bail()
const notEmpty = (before: ValidationChain): ValidationChain => before.notEmpty().withMessage('Cannot be empty').bail()

app.post('/foobar', notEmpty(isString(exists(body('foo'))).trim(), (req: Request, res: Response) => { ... })

I want to do this but chain it instead. Chaining feels much cleaner with express-validator

[gustavohenke]

Hey @ChrisGambrell, unfortunately what you want is not really possible at the moment.
I'll tag it as an enhancement.

In case you're keen on doing the work, I want to offer a different outlook, as I'm not sure what the API/developer experience for a default message should look like.

I think there's an issue or PR somewhere here asking for the validator name to be included in the error object.

So you could do something like this, leveraging withDefaults:

const customValidationResult = validationResult.withDefaults({
	formatter: error => ({
		...error,
		msg: customErrorMessages[error.validatorName],
	})
});