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🚀 New release! Version 4.10.0 is out. 🫣 Get prepared for the upcoming v5.

Image to advertise the release of 4.10.0 of fast-check.

It says:
PREPARE FOR v5.
New plugin API and deprecation notices. v5 is still ahead.

Image build with the help of ChatGPT

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🚀 New release on its way: @fast-check/poisoning v0.3.1 Release notes will land shortly at: github.com/dubzzz/fast-check/releas…

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🚀 New release on its way: @fast-check/vitest v0.5.0 Release notes will land shortly at: github.com/dubzzz/fast-check/releas…

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🚀 New release on its way: @fast-check/jest v2.3.0 Release notes will land shortly at: github.com/dubzzz/fast-check/releas…

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fast-check @fast-check.dev · 23/08/2026

🚀 New release on its way: fast-check v4.10.0 Release notes will land shortly at: github.com/dubzzz/fast-check/releas…

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They sound make it simple for users to come up with their own capabilities. As an example, we have been asked for observability primitives. Plugins have been designed to offer what's needed to cover these needs. They are tailored for extensibility.

fast-check @fast-check.dev · 23/08/2026

🔌 Plugin capabilities coming soon in fast-check. We are currently crafting our first few plugins to confirm the API 🤞 fast-check.dev/docs/core-bl...

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fast-check @fast-check.dev · 18/08/2026

Indeed 😅 Coming soon, we are just preparing the pre-major minor to ease migration and we should be ready 🤞

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fast-check @fast-check.dev · 13/08/2026

🏗️ We are currently thinking and shaping a plugin API to make it easier to extend capabilities of fast-check. We hope it could make it as a minor 🤞 More to come soon...

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fast-check @fast-check.dev · 27/07/2026

⏭️ Iterator's methods being native in JavaScript, we will also reduce our bundle size by dropping our homemade version of them

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fast-check @fast-check.dev · 23/07/2026

🚀 Release note for fast-check 4.9.0 is out. It's all about performance and rewriting of `entityGraph`. More at: fast-check.dev/blog/2026/07...

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fast-check @fast-check.dev · 22/07/2026

⏭️ v5 will also be the first ESM-only release of fast-check. PR on its way 🤞 github.com/dubzzz/fast-...

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fast-check @fast-check.dev · 20/07/2026

In previous majors, there used to be two "opaque" worlds: sync and async one. Each of them came with its own set of configurations. As such there was an `asyncReporter`, an `asyncBeforeEach`... It won't be the case anymore starting at v5.0.0.

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fast-check @fast-check.dev · 19/07/2026

⏭️ In our next major we are gonna make all properties asynchronous. No more questioning about `property` or `asyncProperty` everything will go via `property`.

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fast-check @fast-check.dev · 17/07/2026

We are also thinking about offering sub-imports paths. So one could do both: ```ts import {nat} from 'fast-check' ``` Or: ```ts import {nat} from 'fast-check/arbitraries/nat' ``` The latter is still uncertain for the very first 5.x release.

fast-check @fast-check.dev · 17/07/2026

⏭️ In our next major release we are planning to move away from default exports for named ones. ```ts // Valid import in v4 // import fc from 'fast-check' // New way, already supported in v4 import * as fc from 'fast-check' ```

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Reposted by fast-check

Vladimir @vladimir.berlin · 10/07/2026

`vmThreads` is 30% faster in Vitest 5 for your jsdom tests. It is now a much better alternative to the default forks+jsdom. Vitest 5 also comes with a `vitest doctor` command that will find the best settings for you! As a note, browser mode also becomes ~30% faster, but for different reasons :)

an app with 342 modules + real deps is ~32% faster. 1022 modules + heavier deps is ~28% faster

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fast-check @fast-check.dev · 06/07/2026

We have been verified 🥳

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fast-check @fast-check.dev · 25/06/2026

We just released a bunch of performance optimisations to make both `next` and `jump` methods faster, with a zoom on `jump`. It could drastically decrease what was remaining of the performance overhead induced by fast-check when running your property.

fast-check @fast-check.dev · 25/06/2026

Fresh new version of pure-rand, our backing library powering every random value we generate in fast-check. npmx.dev/package/pure...

npmx.dev

pure-rand - npmx

Pure random number generator written in TypeScript

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fast-check @fast-check.dev · 21/06/2026

Sorry for the inconvenience, I'm adding it back with github.com/dubzzz/fast-.... So far it's not as overall as I'd like

github.com

📝 Add back skills directory by dubzzz · Pull Request #7092 · dubzzz/fast-check

Reverts #7065

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fast-check @fast-check.dev · 20/06/2026

I'll relive it soon. Mostly dropped it by lack to maintain it

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fast-check @fast-check.dev · 16/06/2026

The next minor is being worked on. Expect a few performance optimisations to land ⚡

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Reposted by fast-check

Nicolas Dubien @nicolas.dubien.me · 16/06/2026

I'll discuss a little bit about Property Based Testing and @fast-check.dev during the breakout sessions of @webengineshackfest.org (remotely for me)

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fast-check @fast-check.dev · 04/05/2026

🤫 Direct link to tangled from our documentation

fast-check @fast-check.dev · 04/05/2026

🐒 And now it's fast-check's turn at tangled.org/fast-check.d... So far, just mirrors of @github.com on @tangled.org but stability of GitHub is more and more concerning 😟

tangled.org

fast-check.dev/fast-check

[[MIRROR from GitHub]] Property based testing framework for JavaScript (like QuickCheck) written in TypeScript

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Reposted by fast-check

Bjorn Lu @bluwy.me · 14/04/2026

FYI if you use pnpm and upgraded from Vite 7 -> 8, you might still have esbuild installed but unused. You can purge it out by: 1. Set `autoInstallPeers: false` in `pnpm-workspace.yaml` 2. `pnpm i` 3. Undo no1 4. `pnpm i`

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fast-check @fast-check.dev · 28/03/2026

You mean fast-check? Maybe our quick start could help to get more about it: fast-check.dev/docs/tutoria...

fast-check.dev

Basic Setup | fast-check

Setup your environment

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🚀 We just released a fresh way lighter version of pure-rand. Install size for each recent version: • 𝟴.𝟰.𝟬: 62.4 kB 🐇 • 𝟴.𝟯.𝟬: 71.6 kB 🐘 • 𝟴.𝟮.𝟬: 53.6 kB 🐜

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So far it comes with a few limitations that we have not overcome yet. The clean up of the first beforeEach is fully handled by vitest, as such you'll see the second beforeEach and it's clean up being executed before the first clean up gets called.

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@fast-check/vitest - npmx

🖇️ Our latest release of @fast-check/vitest added native support for before each/afterEach hooks of @vitest.dev. No more need to manually connect them into fast-check assertions they get automatically integrated if you use our connector package. Connector: npmx.dev/package/@fas...

npmx.dev

Property based testing for Vitest based on fast-check

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fast-check @fast-check.dev · 20/03/2026

🗜️ We are working on a new release of pure-rand to decrease the bundle impact of our Mersenne Twister jump 🤫 📚 And on fast-check's side we pile a few ideas for a next major that should bring an even faster runtime and more.

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🎲 New release of pure-rand, our internal dependency. With 33% increase in bundle size but for the right cause: we want to provide users with ways to jump on Mersenne Twister generators. It has been a long PR started 6 years ago and that finally made it.

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fast-check @fast-check.dev · 05/03/2026

🚀 This is it: version 8.0.0 of pure-rand is out! 📦 Lighter bundle 🛢️ No more barrel files 🧹 Simplified API by default npmx.dev/package/pure...

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Good idea 💡 I'm gonna think about it. Definitely something worth providing to ease the creation of multiple random streams.

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The next major is currently under active development and should come with several new distributions and maybe a few extra generators. But for generators we will have to carefully benchmark them one by one to keep our high throughput standard

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To date pure-rand is the fastest random generator library on npm. And it comes with plenty of built-in generators and distributions (to pull data outside of generators)

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We are currently trying to solve most of the issues that made the #faker project copy paste the code directly in their source code a few years ago

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Still wondering if we should go full ESM for it. The library is being used by #Jest so we are not sure we do that given they don't support require(esm)

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