Requirements

@traversable/typebox has a peer dependency on TypeBox (v0.34).

Getting started

$ pnpm add @traversable/typebox @sinclair/typebox

Here's an example of importing the library:

import * as T from '@sinclair/typebox'
import { box } from '@traversable/typebox'

// or, if you prefer, you can use named imports:
import { deepClone, deepEqual } from '@traversable/typebox'

// see below for specific examples

Table of contents

Fuzz-tested, production ready

• box.deepClone
• box.deepClone.writeable
• box.deepEqual
• box.deepEqual.writeable

Advanced

• box.fold
• box.Functor

Features

box.deepClone

box.deepClone lets users derive a specialized "deep copy" function that works with values that have been already validated.

Because the values have already been validated, clone times are significantly faster than alternatives like window.structuredClone and Lodash.cloneDeep.

Performance comparison

Here's a Bolt sandbox if you'd like to run the benchmarks yourself.

                           ┌─────────────────┐
                           │         (avg)   │
┌──────────────────────────┼─────────────────┤
│  Lodash.cloneDeep        │  31.32x faster  │
├──────────────────────────┼─────────────────┤
│  window.structuredClone  │  54.36x faster  │
└──────────────────────────┴─────────────────┘

This article goes into more detail about what makes box.deepClone so fast.

Example

import * as T from '@sinclair/typebox'
import { box } from '@traversable/typebox'

const Address = T.Object({
  street1: T.String(),
  street2: T.Optional(T.String()),
  city: T.String(),
})

const deepClone = box.deepClone(Address)
const deepEqual = box.deepEqual(Address)

const sherlock = { street1: '221 Baker St', street2: '#B', city: 'London' }
const harry = { street1: '4 Privet Dr', city: 'Little Whinging' }

const sherlockCloned = deepClone(sherlock)
const harryCloned = deepClone(harry)

deepEqual(sherlockCloned, sherlock) // => true
deepEqual(harryCloned, harry)       // => true

sherlock === sherlockCloned         // => false
harry === harryCloned               // => false

See also

• box.deepClone.writeable

box.deepClone.writeable

box.deepClone.writeable lets users derive a specialized "deep clone" function that works with values that have been already validated.

Compared to box.deepClone, box.deepClone.writeable returns the clone function in stringified ("writeable") form.

Example

import { box } from '@traversable/typebox'

const deepClone = box.deepClone.writeable({
  type: 'object',
  required: ['street1', 'city'],
  properties: {
    street1: { type: 'string' },
    street2: { type: 'string' },
    city: { type: 'string' },
  }
}, { typeName: 'Address' })

console.log(deepClone) 
// =>
// type Address = { street1: string; street2?: string; city: string; }
// function deepClone(prev: Address): Address {
//   return {
//     street1: prev.street1,
//     ...prev.street2 !== undefined && { street2: prev.street2 },
//     city: prev.city
//   }
// }

See also

• box.deepClone

box.deepEqual

box.deepEqual lets users derive a specialized "deep equal" function that works with values that have been already validated.

Because the values have already been validated, comparison times are significantly faster than alternatives like NodeJS.isDeepStrictEqual and Lodash.isEqual.

Performance comparison

Here's a Bolt sandbox if you'd like to run the benchmarks yourself.

                             ┌────────────────┬────────────────┐
                             │   Array (avg)  │  Object (avg)  │
┌────────────────────────────┼────────────────┼────────────────┤
│  NodeJS.isDeepStrictEqual  │  40.3x faster  │  56.5x faster  │
├────────────────────────────┼────────────────┼────────────────┤
│  Lodash.isEqual            │  53.7x faster  │  60.1x faster  │
└────────────────────────────┴────────────────┴────────────────┘

This article goes into more detail about what makes box.deepEqual so fast.

Notes

• Best performance
• Works in any environment that supports defining functions using the Function constructor, including (as of May 2025) Cloudflare workers 🎉

Example

import { box } from '@traversable/typebox'

const deepEqual = box.deepEqual({
  type: 'object',
  required: ['street1', 'city'],
  properties: {
    street1: { type: 'string' },
    street2: { type: 'string' },
    city: { type: 'string' },
  }
})

deepEqual(
  { street1: '221B Baker St', city: 'London' },
  { street1: '221B Baker St', city: 'London' }
) // => true

deepEqual(
  { street1: '221B Baker St', city: 'London' },
  { street1: '4 Privet Dr', city: 'Little Whinging' }
) // => false

See also

• box.deepEqual.writeable

box.deepEqual.writeable

box.deepEqual.writeable lets users derive a specialized "deep equal" function that works with values that have been already validated.

Compared to box.deepEqual, box.deepEqual.writeable returns the deep equal function in stringified ("writeable") form.

Notes

• Useful when you're consuming a set of TypeBox schemas and writing all them to disc somewhere
• Also useful for testing purposes or for troubleshooting, since it gives you a way to "see" exactly what the deepEqual functions are doing

Example

import { box } from '@traversable/typebox'

const deepEqual = box.deepEqual.writeable({
  type: 'object',
  required: ['street1', 'city'],
  properties: {
    street1: { type: 'string' },
    street2: { type: 'string' },
    city: { type: 'string' },
  }
}, { typeName: 'Address' })

console.log(deepEqual)
// =>
// type Address = { street1: string; street2?: string; city: string; }
// function deepEqual(x: Address, y: Address) {
//   if (x === y) return true;
//   if (x.street1 !== y.street1) return false;
//   if (x.street2 !== y.street2) return false;
//   if (x.city !== y.city) return false;
//   return true;
// }

See also

• box.deepEqual

box.fold

[!NOTE] box.fold is an advanced API.

Use box.fold to define a recursive traversal of a TypeBox schema. Useful when building a schema rewriter.

What does it do?

Writing an arbitrary traversal with box.fold is:

1. non-recursive
2. 100% type-safe

The way it works is pretty simple: if you imagine all the places in the TypeBox schema that are recursive, those "holes" will be the type that you provide via type parameter.

Example

Let's write a function that takes an arbitrary TypeBox schema, and generates mock data that satisfies the schema (a.k.a. a "faker").

[!NOTE] You can play with this example on StackBlitz

import * as T from '@sinclair/typebox'
import { faker } from '@faker-js/faker'
import { F, tagged } from '@traversable/typebox'

type Fake = () => unknown

const fake = F.fold<Fake>((x) => {
  //                𐙘__𐙘 this type parameter fills in the "holes" below
  switch (true) {
    case tagged('array')(x): return () => faker.helpers.multiple(
      () => x.items()
      //       ^? method items: Fake
      //                        𐙘__𐙘
    )
    case tagged('never')(x): return () => void 0
    case tagged('unknown')(x): return () => void 0
    case tagged('any')(x): return () => void 0
    case tagged('void')(x): return () => void 0
    case tagged('null')(x): return () => null
    case tagged('undefined')(x): return () => undefined
    case tagged('symbol')(x): return () => Symbol()
    case tagged('boolean')(x): return () => faker.datatype.boolean()
    case tagged('integer')(x): return () => faker.number.int()
    case tagged('bigInt')(x): return () => faker.number.bigInt()
    case tagged('number')(x): return () => faker.number.float()
    case tagged('string')(x): return () => faker.lorem.words()
    case tagged('date')(x): return () => faker.date.recent()
    case tagged('literal')(x): return () => x.const
    case tagged('allOf')(x): return () => Object.assign({}, ...x.allOf)
    case tagged('anyOf')(x): return () => faker.helpers.arrayElement(x.anyOf.map((option) => option()))
    case tagged('optional')(x): return () => faker.helpers.arrayElement([x.schema, undefined])
    case tagged('tuple')(x): return () => x.items.map((item) => item())
    case tagged('record')(x): return () => Object.fromEntries(Object.entries(x.patternProperties).map(([k, v]) => [k, v()]))
    case tagged('object')(x): return () => Object.fromEntries(Object.entries(x.properties).map(([k, v]) => [k, v()]))
    default: { x satisfies never; throw Error('Unsupported schema') }
    //         𐙘_______________𐙘
    //        exhaustiveness check works
  }
})

// Let's test it out:
const mock = fake(
  T.Object({
    abc: T.Array(T.String()), 
    def: T.Optional(
      T.Tuple([
        T.Number(), 
        T.Boolean()
      ])
    )
  })
)

console.log(mock())
// => {
//  abc: [
//     'annus iure consequatur',
//     'aer suus autem',
//     'delectus patrocinor deporto',
//     'benevolentia tonsor odit',
//     'stabilis dolor tres',
//     'mollitia quibusdam vociferor'
//   ],
//   def: [-882, false]
// }

Theory

box.fold is similar to, but more powerful than, the visitor pattern.

If you're curious about the theory behind it, its implementation was based on a 1991 paper called Functional Programming with Bananas, Lenses, Envelopes and Barbed Wire.

See also

• box.Functor

box.Functor

[!NOTE] box.Functor is an advanced API.

box.Functor is the primary abstraction that powers @traversable/typebox.

box.Functor is a powertool. Most of @traversable/typebox uses box.Functor under the hood.

Compared to the rest of the library, it's fairly "low-level", so unless you're doing something pretty advanced you probably won't need to use it directly.

See also

• box.fold