Value.clone and Value.hash

Pure static utilities that work on any value without a schema.

---

Value.clone

Declaration. Deep-copies a value using structuredClone. Returns an independent copy with no shared object references. Type-preserving - clone<T>(v: T): T.

Use this when you need an independent copy before passing a value to a mutating operation, or before Value.diff when you want to keep the original. instantiate() already clones internally; only call clone when doing your own mutation.

Don't use this when you just need a shallow copy (use { ...obj } instead). Don't use it for non-JSON-serializable values (functions, class instances with methods - structuredClone may throw or strip those).

Examples

Example 1: Clone an order before adding a line item

import { Value } from 'json-tology';
import { bookstoreEntities as entities, OrderSchema } from './bookstore/index.js';

const order = jt.instantiate(OrderSchema.$id, {
  id:         'a1b2c3d4-e5f6-7890-abcd-ef1234567890',
  customerId: 'c1a2b3d4-e5f6-7890-abcd-ef1234567890',
  placedAt:   '2026-01-15T10:30:00Z',
  total:      14.99,
  items:      [{ bookIsbn: '9780140449136', quantity: 1, unitPrice: 14.99 }],
});

const copy = Value.clone(order);
(copy.items as Array<{ bookIsbn: string; quantity: number; unitPrice: number }>).push(
  { bookIsbn: '9780062316110', quantity: 1, unitPrice: 9.99 }
);

console.log(order.items.length); // 1  - original unchanged
console.log(copy.items.length);  // 2

Example 2: Clone nested addresses

const customer = jt.instantiate(CustomerSchema.$id, {
  id:        'c1a2b3d4-e5f6-7890-abcd-ef1234567890',
  email:     'alice@bookstore.example',
  name:      'Alice Chen',
  addresses: [{ street: '12 Elm Lane', city: 'Bookham', postalCode: '94107' }],
});

const copy = Value.clone(customer);
console.log(copy.addresses === customer.addresses); // false  - deep copy

Comparison

json-tology

const copy = Value.clone(order); // deep copy via structuredClone

Zod

// No built-in clone utility.
const copy = structuredClone(order);

Valibot

// Limitation: Valibot has no clone utility - use structuredClone.
const copy = structuredClone(order);

TypeBox + Value

import { Value } from '@sinclair/typebox/value';
const copy = Value.Clone(order);

AJV

// No built-in clone  - use structuredClone.
const copy = structuredClone(order);

Pydantic

copy = order.model_copy(deep=True)

---

Value.hash

Declaration. Computes a deterministic FNV-1a hash of a JSON-serializable value. Property key order is normalized before hashing - two objects with the same keys/values but different key order produce identical hashes. Returns a hex string. Not cryptographically secure.

Use this when you need content-addressable caching, deduplication, ETag generation, or change detection without a full structural diff.

Don't use this when you need cryptographic security - this is not a secure hash. Don't use it for values that contain non-JSON-serializable data (functions, undefined, circular references - behavior is undefined).

Examples

Example 1: Generate an ETag for a book

const book = jt.instantiate(BookSchema.$id, {
  isbn:    '9780140449136',
  title:   'Crime and Punishment',
  authors: ['Fyodor Dostoevsky'],
  price:   14.99,
});

const etag = Value.hash(book);
// deterministic hex string  - same value each time, key order independent

const h1 = Value.hash({ isbn: '9780140449136', title: 'Crime and Punishment' });
const h2 = Value.hash({ title: 'Crime and Punishment', isbn: '9780140449136' });
console.log(h1 === h2); // true  - key order doesn't matter

Example 2: Cache invalidation

const prevHash = Value.hash(order);
// ... order is updated ...
const newOrder = jt.instantiate(OrderSchema.$id, { ...order, total: 27.98 });

if (Value.hash(newOrder) !== prevHash) {
  invalidateCache(order.id);
}

Comparison

json-tology

Value.hash(book) // deterministic FNV-1a hex, key-order invariant

Zod

// No built-in hash utility.
// Use a third-party library: object-hash, stable-hash, etc.
import hash from 'object-hash';
const h = hash(book);

Valibot

// Limitation: Valibot has no hash utility.
// Use a third-party library: object-hash, stable-hash, etc.
import hash from 'object-hash';
const h = hash(book);

TypeBox + Value

// No built-in hash utility.

AJV

// No built-in hash utility.

Pydantic

import hashlib, json
data = book.model_dump()
h = hashlib.sha256(json.dumps(data, sort_keys=True).encode()).hexdigest()

Related

• Value.diff - compute structural differences between two values
• Value.clone - deep copy before mutation or diffing

See also

• Bookstore domain - where Order, Book, Customer are defined