ArkType 2 schemas with morphs, narrows and discriminated unions: working versions (tested 2026-10-15)

{
  "name": "arktype-schema-validation",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node --import tsx --test test/*.test.ts"
  },
  "dependencies": {
    "arktype": "2.2.8"
  },
  "devDependencies": {
    "@types/node": "26.6.5",
    "tsx": "4.23.15"
  }
}

import { type } from "arktype";

export const User = type({
  email: "string.email",
  name: "string > 0",
  age: "number.integer >= 13",
  role: "'admin' | 'member' | 'guest'",
});

export const CreateUser = type({
  email: "string.email",
  name: "string > 0",
  "age?": "number.integer >= 13",
  role: "'admin' | 'member' | 'guest' = 'member'",
}).pipe((u) => ({ ...u, age: u.age ?? 18 }));

export const Event = type({
  "+": "reject",
  kind: "'created'",
  id: "string > 0",
}).or({
  "+": "reject",
  kind: "'deleted'",
  id: "string > 0",
  reason: "string > 0",
});

export function parseUser(input: unknown) {
  const out = User(input);
  if (out instanceof type.errors) return { ok: false as const, problems: out.summary };
  return { ok: true as const, data: out };
}

import { test } from "node:test";
import assert from "node:assert/strict";
import { CreateUser, Event, parseUser, User } from "../src/user.ts";
import { type } from "arktype";

test("accepts a valid user", () => {
  const r = parseUser({ email: "[email protected]", name: "Ada", age: 30, role: "admin" });
  assert.equal(r.ok, true);
  if (r.ok) assert.equal(r.data.name, "Ada");
});

test("rejects bad email with problems summary", () => {
  const r = parseUser({ email: "nope", name: "Ada", age: 30, role: "member" });
  assert.equal(r.ok, false);
  if (!r.ok) assert.match(r.problems, /email/i);
});

test("CreateUser morph fills default age and role", () => {
  const out = CreateUser({ email: "[email protected]", name: "Bob" });
  assert.equal(out instanceof type.errors, false);
  if (!(out instanceof type.errors)) {
    assert.equal(out.age, 18);
    assert.equal(out.role, "member");
  }
});

test("discriminated Event union", () => {
  const ok = Event({ kind: "deleted", id: "1", reason: "spam" });
  assert.equal(ok instanceof type.errors, false);
  const bad = Event({ kind: "deleted", id: "1" });
  assert.equal(bad instanceof type.errors, true);
  const extra = Event({ kind: "created", id: "1", extra: true });
  assert.equal(extra instanceof type.errors, true);
});