Introducing: @traversable/zod

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

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

Note:
Currently @traversable/zod only works with the latest version of Zod (v4).

Cover photo credit:
Jack Noble, Mob Psycho 100 モブサイコ100

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What makes @traversable/zod different?

@traversable/zod can be used in 2 ways:

1. Pick one of over 25 transformers available off-the-shelf
2. Hand-roll your own custom transformer

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Off-the-shelf

ᯓ📦 zx.check

• Converts a Zod schema into a super-performant type-guard

• 📖 Performance profile

ᯓ📦 zx.deepClone

• Converts a Zod schema into a "deep copy" function

• 📖 How I built JavaScript's fastest deep clone function

ᯓ📦 zx.deepEqual

• Converts a Zod schema into a "deep equal" function

• 📖 How I built JavaScript's fastest deep equals function

ᯓ📦 zx.deepPartial

• Makes all the properties of a Zod schema optional

• 📖 Zod drops deepPartial in v4

ᯓ📦 zx.toString

• Converts a Zod schema into a string

• Useful for testing, codegen, sanity checking

ᯓ📦 zx.toType

• Converts a Zod schema into a TypeScript type

• Preserves schema metadata as JSDoc annotations

ᯓ📦 zx.makeLens

• 🔍 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

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Roll your own

ᯓ📦 zx.fold

All the off-the-shelf transformers that @traversable/zod ships are powered by zx.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 toJsonSchema.

The implementation is so minimal (28 lines!) that I've embedded it here, in its entirety:

Note:

I specifically chose toJsonSchema because multiple libraries already exist that do this, including Zod itself.

The goal is to showcase how you can use zx.fold to build a library of your own.

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Closing thoughts

Thanks for reading!

If you have any feedback, feature requests, or questions, feel free to open an issue or start a discussion.

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Links

1. @traversable/zod on GitHub
2. The full toJsonSchema demo

Comments

[Ben Halpern]

Good stuff

[andrew jarrett]

Thanks for reading!

[Anna kowoski]

Nice Article Andrew!

[andrew jarrett]

Thanks!

[Katerina]

Looks cool, but sandbox steals my input focus is annoying

[andrew jarrett]

Ack! I don't know how to fix this. Might just rip it out and use a code block