Simple custom error message

[SlavenIvanov]

Request a feature

Is it possible to add a simple error message to a field?

🤷 Motivation

It would be great to simply setup a default error message.

💡 Solution

export const project = type({
	name: "string: errorMsg:'Name must be a string 👽'" // or anything that can solve this issue.
})

[ssalbdivad]

Good question! I'm working on the docs for v2 now but error messages are very customizable!

Here are a few options for this situation:

import { type } from "arktype"

export const project = type({
	name: ["string", "@", "a string 👽"]
})

const out = project({ name: 5 })

if (out instanceof type.errors) {
	// 'name must be a string 👽 (was number)'
	console.log(out.summary)
} else {
	console.log(`Hi, ${out.name}!`)
}

const name = type("string").describe("a string 👽")

// this is equivalent to above
const project2 = type({ name })

Note that what you pass to describe is essentially the ___ in must be ___. This allows error messages to compose better for unions, intersections etc.

There are ways to customize the full structure of the message but I will get into those more in the upcoming docs!