ArkType

ArkType

This skill explains how to use ArkType, a validation library for TypeScript. Read this skill when writing validation logic using ArkType. ArkType is a library that allows you to validate values ​​using a notation very similar to that of TypeScript type definitions.

Installation

If ArkType is not yet present in the project's dependencies, you can install it with npm install arktype. If the project uses a package manager other than npm, use that instead.

Basic usage

import { type } from "arktype";

const User = type({
    name: "string",
    platform: "'android' | 'ios'",
    email: "string.email",
    score: "number.integer <= 100",
    "versions?": "(number | string)[]",
    details: {
        // nested definitions don't need to be wrapped
        "['devices' | 'apps']": "string[]"
    },
    "areWeCoolYet": "boolean = true"
});

// extract the type if needed
type User = typeof User.infer;

const out = User(value);

if (out instanceof type.errors) {
    console.error(out.summary);
} else {
    console.log(`Hello, ${out.name}`);
}

// throws an error if the value is invalid.
const user = User.assert(value);

// `.allows()` is a type guard and does not apply morphs or transformations
if (User.allows(value)) {
    console.log("value is correct");
}

Note: Object types allow and preserve undeclared properties by default. Use "+": "reject" to reject them or "+": "delete" to strip them.

Optional properties

Optional properties does not implicitly allow undefined as a value.

const User = type({
    // `name` may be absent
    "name?": "string",
    // `value` is required, but may be undefined
    value: "string | undefined",
    // `label` may be absent or explicitly undefined
    "label?": "string | undefined"
});

Constraints

// you can add non-standard constraints with `.narrow()`
const Odd = type("number").narrow((n, ctx) =>
    n % 2 === 0 ? ctx.mustBe("odd") : true
);

Builtin keywords

In ArkType, for example, you can represent a URL-formatted string with type("string.url"), and you can morph it into a URL object while performing validation using type("string.url.parse").