andrew jarrett

Posted on Sep 15

Introducing: @traversable/valibot

#typescript #javascript #webdev #opensource

A few weeks ago I released a TypeScript library called @traversable/valibot.

This post covers what the library does, and highlights a few of its unique features.

Cover photo credit:
Astro Boy Schematics (鉄腕アトム), Tezuka Productions

Note:
Currently @traversable/valibot only works with the latest version of Valibot (v1.1).

What makes @traversable/valibot different?

@traversable/valibot can be used in 2 ways:

Pick one of over 15 transformers available off-the-shelf
Hand-roll your own custom transformer

Off-the-shelf

ᯓ🚀 `vx.check`

Turn a Valibot schema into a super-performant type-guard
📖 Performance profile

ᯓ🚀 `vx.deepClone`

Converts a Valibot schema into a “deep copy” function
📖 How I built JavaScript's fastest deep clone function

ᯓ🚀 `vx.deepEqual`

Converts a Valibot schema into a “deep equal” function
📖 How I built JavaScript's fastest deep equals function

ᯓ🚀 `vx.toString`

Converts a Valibot schema into a string
Useful for testing, codegen, sanity checking

ᯓ🚀 `vx.toType`

Converts a Valibot schema into a TypeScript type
🏷️ Preserves schema metadata as JSDoc annotations

ᯓ🚀 `vx.defaultValue` ✨new!✨

Derive a configurable default value from a schema
Designed for schema-driven forms on the frontend

ᯓ🚀 `vx.makeLens` ✨coming soon!✨

🔍 Focus nested values with lenses (getters/setters)
🌈 Reify control flow with prisms (pattern-matchers)
⛰️ Map over containers with traversals (for-loops)
🧱 Stack them together with function composition

Roll your own

ᯓ🚀 `vx.fold`

All the off-the-shelf transformers that @traversable/valibot ships are powered by vx.fold.

Under the hood, the library uses an abstraction called recursion schemes that make implementing recursion simple and fun.

To demonstrate, I used it to implement a mock data generator.

The implementation is so minimal (25 lines!) that I've embedded it here, in its entirety:

Note:

To keep things simple, this is a partial implementation.

For a more robust version, see this StackBlitz.

Bonus: @traversable/valibot-test

@traversable/valibot-test is a testing library built specifically for library authors who are building on top of Valibot.

Under the hood, it uses a TypeScript library called fast-check to generate random Valibot schemas.

Being able to generate random schemas turns out to be incredibly useful for fuzz testing.

For example, here we use it to test that our valibotToFaker function always generates valid data:

💡 Tip:

Scroll up in the terminal panel to see the generated schemas + mock data!

Updates

Update: as of yesterday, @traversable/valibot is part of the Valibot ecosystem!

doc: adds `@traversable/valibot` and `@traversable/valibot-test` to ecosystem #1298

ahrjarrett posted on Sep 07, 2025

Hello Valibot maintainers!

This PR adds 2 libraries to the ecosystem:

These libraries were primarily built for developers who are building tools on top of Valibot, but can also be used for one of the 10+ off-the-shelf transformers that we currently support.

Happy to talk more about the library if you have any questions!

View on GitHub

Comment for #1298

fabian-hiller commented on Sep 13, 2025

Thank you! And sorry for the late reaction! What you have built looks amazing! Should we do a post on social media?

View on GitHub

The Valibot ecosystem is by far the most welcoming and collaborative TypeScript schema community out there, so I'm super proud to be able to contribute back ☺️.