js-yaml 5 config files validated with Zod 4: working versions (tested 2026-10-15)

{
  "name": "js-yaml-zod-config",
  "private": true,
  "type": "module",
  "scripts": {
    "test": "node --import tsx --test test/*.test.ts"
  },
  "dependencies": {
    "js-yaml": "5.4.3",
    "zod": "4.6.7"
  },
  "devDependencies": {
    "@types/node": "26.6.5",
    "tsx": "4.23.15",
    "@types/js-yaml": "4.0.9"
  }
}

import { load } from "js-yaml";
import { z } from "zod";

export const AppConfig = z.object({
  name: z.string().min(1),
  port: z.number().int().min(1).max(65535).default(3000),
  features: z.object({
    billing: z.boolean().default(false),
    beta: z.boolean().default(false),
  }).default({ billing: false, beta: false }),
  database: z.object({
    url: z.string().min(1),
    pool: z.number().int().positive().default(5),
  }),
});

export type AppConfig = z.infer<typeof AppConfig>;

export function loadConfig(source: string): AppConfig {
  const raw = load(source);
  return AppConfig.parse(raw);
}

export function safeLoadConfig(source: string) {
  const raw = load(source);
  const r = AppConfig.safeParse(raw);
  if (!r.success) return { ok: false as const, issues: z.flattenError(r.error).fieldErrors };
  return { ok: true as const, data: r.data };
}

import { test } from "node:test";
import assert from "node:assert/strict";
import { loadConfig, safeLoadConfig } from "../src/config.ts";

const good = `
name: provenpin
database:
  url: "sqlite://:memory:"
features:
  billing: true
`;

test("loads yaml with defaults", () => {
  const cfg = loadConfig(good);
  assert.equal(cfg.name, "provenpin");
  assert.equal(cfg.port, 3000);
  assert.equal(cfg.features.billing, true);
  assert.equal(cfg.features.beta, false);
  assert.equal(cfg.database.pool, 5);
});

test("rejects missing database", () => {
  const r = safeLoadConfig("name: x\n");
  assert.equal(r.ok, false);
  if (!r.ok) assert.ok(r.issues.database);
});

test("rejects bad types", () => {
  const r = safeLoadConfig("name: x\nport: nope\ndatabase:\n  url: u\n");
  assert.equal(r.ok, false);
});