Error Provider

There are 2 ways to provide a custom error message when the validation fails:

1. inline message property
2. Using onError event

Message Property

TypeBox offers an additional "error" property, allowing us to return a custom error message if the field is invalid.

import { Elysia, t } from 'elysia'

new Elysia()
    .get('/', () => 'Hello World!', {
        body: t.Object(
            {
                x: t.Number()
            },
            {
                error: 'x must be a number'
            }
        )
    })
    .listen(3000)

The following is an example of usage of the error property on various types:

TypeBox	Error
t.String({ format: 'email', error: 'Invalid email :(' })	Invalid Email :(
t.Array( t.String(), { error: 'All members must be a string' } )	All members must be a string
t.Object({ x: t.Number() }, { error: 'Invalid object UwU' })	Invalid object UwU

onError

We can customize the behavior of validation based on onError event by narrowing down the error code call "VALIDATION".

import { Elysia, t } from 'elysia'

new Elysia()
	.onError(({ code, error }) => {
		if (code === 'VALIDATION')
		    return error.message
	})
	.listen(3000)

Narrowed down error type, will be typed as ValidationError imported from 'elysia/error'.

ValidationError exposed a property name validator typed as TypeCheck, allowing us to interact with TypeBox functionality out of the box.

import { Elysia, t } from 'elysia'

new Elysia()
    .onError(({ code, error }) => {
        if (code === 'VALIDATION')
            return error.validator.Errors(error.value).First().message
    })
    .listen(3000)

Error list

ValidationError provides a method ValidatorError.all, allowing us to list all of the error causes.

import { Elysia, t } from 'elysia'

new Elysia()
	.post('/', ({ body }) => body, {
		body: t.Object({
			name: t.String(),
			age: t.Number()
		}),
		error({ code, error }) {
			switch (code) {
				case 'VALIDATION':
                    console.log(error.all)

                    // Find a specific error name (path is OpenAPI Schema compliance)
					const name = error.all.find((x) => x.path === '/name')

                    // If has a validation error, then log it
                    if(name)
    					console.log(name)
			}
		}
	})
	.listen(3000)

For more information about TypeBox's validator, see TypeCheck.