Szymon Chmal
@chmal.it
Dev Lead / Senior React Native Developer x Callstack | Microsoft MVP | Speaker | GDG Toruń Leader
The Jest integration I sneak-peeked earlier is also letting me roll out code coverage support. The coverage reporter is already in place. I just had to instrument the code and send the coverage data from the device back to the CLI. Surprisingly, it was really easy to implement!
October 20, 2025 at 4:07 PM
The Jest integration I sneak-peeked earlier is also letting me roll out code coverage support. The coverage reporter is already in place. I just had to instrument the code and send the coverage data from the device back to the CLI. Surprisingly, it was really easy to implement!
Harness isn't a simple tool - it's a bunch of components working together to give the best DX for testing JS code with native modules. Maintaining all that as a solo dev isn't easy, so I tried offloading some work by using Jest's CLI to run Harness… and it worked!
October 17, 2025 at 7:32 PM
Harness isn't a simple tool - it's a bunch of components working together to give the best DX for testing JS code with native modules. Maintaining all that as a solo dev isn't easy, so I tried offloading some work by using Jest's CLI to run Harness… and it worked!
We're hosting a livestream today, with a special focus on React Native Harness! Expect insider insights on how it all works and sneak peeks at what's coming next.
🗓️ Thu 16, 5 PM CEST
See you there!
🗓️ Thu 16, 5 PM CEST
See you there!
October 16, 2025 at 9:27 AM
We're hosting a livestream today, with a special focus on React Native Harness! Expect insider insights on how it all works and sneak peeks at what's coming next.
🗓️ Thu 16, 5 PM CEST
See you there!
🗓️ Thu 16, 5 PM CEST
See you there!
🎉 Introducing React Native Harness - a lightweight framework for testing native modules directly on device or emulator.
Write tests in a Jest-like syntax, run them in a real React Native runtime, and verify native behavior without mocks.
Write tests in a Jest-like syntax, run them in a real React Native runtime, and verify native behavior without mocks.
October 15, 2025 at 1:59 PM
🎉 Introducing React Native Harness - a lightweight framework for testing native modules directly on device or emulator.
Write tests in a Jest-like syntax, run them in a real React Native runtime, and verify native behavior without mocks.
Write tests in a Jest-like syntax, run them in a real React Native runtime, and verify native behavior without mocks.
Are you using the Performance API in React Native? If yes, I'm pretty sure you've wished a bunch of times that you could check out measures like you do in Chrome DevTools. What if I told you Rozenite is about to bring you that same vibe? Hot or not?
August 12, 2025 at 10:07 AM
Are you using the Performance API in React Native? If yes, I'm pretty sure you've wished a bunch of times that you could check out measures like you do in Chrome DevTools. What if I told you Rozenite is about to bring you that same vibe? Hot or not?
Yesterday, the community requested server-side event support for Rozenite's Network Activity. I said I'd look into it… but somehow ended up pushing a branch with the feature almost done. Whoops! 🙈
August 6, 2025 at 3:47 PM
Yesterday, the community requested server-side event support for Rozenite's Network Activity. I said I'd look into it… but somehow ended up pushing a branch with the feature almost done. Whoops! 🙈
The Rozenite plugin family is growing, so I created a plugin directory!
It includes both official plugins and community ones like rozenite-preview.
Best part? You can add your own by opening a quick pull request on the Rozenite repo.
It includes both official plugins and community ones like rozenite-preview.
Best part? You can add your own by opening a quick pull request on the Rozenite repo.
August 6, 2025 at 9:25 AM
The Rozenite plugin family is growing, so I created a plugin directory!
It includes both official plugins and community ones like rozenite-preview.
Best part? You can add your own by opening a quick pull request on the Rozenite repo.
It includes both official plugins and community ones like rozenite-preview.
Best part? You can add your own by opening a quick pull request on the Rozenite repo.
Just found out I'll be speaking at React Universe Conf!
Rozenite's been out for a while, but in this talk, I'll dive deeper into how it works under the hood - how I hooked into DevTools without forking anything, and how you can build your own plugins too.
Hope to see you there!
Rozenite's been out for a while, but in this talk, I'll dive deeper into how it works under the hood - how I hooked into DevTools without forking anything, and how you can build your own plugins too.
Hope to see you there!
August 4, 2025 at 4:25 PM
Just found out I'll be speaking at React Universe Conf!
Rozenite's been out for a while, but in this talk, I'll dive deeper into how it works under the hood - how I hooked into DevTools without forking anything, and how you can build your own plugins too.
Hope to see you there!
Rozenite's been out for a while, but in this talk, I'll dive deeper into how it works under the hood - how I hooked into DevTools without forking anything, and how you can build your own plugins too.
Hope to see you there!
New week, new feature! Struggling to understand what's going on in your WebSocket connection? Fear not! Thanks to Rozenite, you'll soon be able to inspect WebSocket traffic and review each message one by one - whether it's text, binary, or JSON. Coming soon 🔥
August 4, 2025 at 11:18 AM
New week, new feature! Struggling to understand what's going on in your WebSocket connection? Fear not! Thanks to Rozenite, you'll soon be able to inspect WebSocket traffic and review each message one by one - whether it's text, binary, or JSON. Coming soon 🔥
Bronze trophy unlocked: 100 stars collected!
It's not platinum (yet), but every legend starts somewhere 😉
It's not platinum (yet), but every legend starts somewhere 😉
August 1, 2025 at 4:28 PM
Bronze trophy unlocked: 100 stars collected!
It's not platinum (yet), but every legend starts somewhere 😉
It's not platinum (yet), but every legend starts somewhere 😉
Rozenite's Network Activity plugin got a major overhaul yesterday! The new UI and improved functionality make it much more convenient to use. You can now inspect request bodies and responses with an interactive JSON viewer 🚀
August 1, 2025 at 12:53 PM
Rozenite's Network Activity plugin got a major overhaul yesterday! The new UI and improved functionality make it much more convenient to use. You can now inspect request bodies and responses with an interactive JSON viewer 🚀
Rozenite is gaining traction - we've just crossed 50 stars on GitHub, and the number is steadily rising! It was included in the latest edition of the This Week in React newsletter, so if you slept through the release, it's high time you gave it a try and left a star while you're at it 🌟
This Week In React 245
🍿 Read/subscribe here: thisweekinreact.com/newsletter/245
⚛️ React:
- TanStack
- React Core
- Next MCP
- RSC
- memo
- Remix
- Base UI
- React Aria
📱 RN:
- Precompiled iOS
- Rozenite
- AI
- Perf
- Nitro
- BottomSheet
- Tinybase
🍿 Read/subscribe here: thisweekinreact.com/newsletter/245
⚛️ React:
- TanStack
- React Core
- Next MCP
- RSC
- memo
- Remix
- Base UI
- React Aria
📱 RN:
- Precompiled iOS
- Rozenite
- AI
- Perf
- Nitro
- BottomSheet
- Tinybase
July 30, 2025 at 6:06 PM
Rozenite is gaining traction - we've just crossed 50 stars on GitHub, and the number is steadily rising! It was included in the latest edition of the This Week in React newsletter, so if you slept through the release, it's high time you gave it a try and left a star while you're at it 🌟
Redux DevTools plugin for Rozenite is nearly complete. It offers basic debugging functionality, though without time travel or action dispatch capabilities. There's an upstream issue with the package that needs to be addressed first.
github.com/callstackinc...
github.com/callstackinc...
feat: introduce Redux Devtools plugin by V3RON · Pull Request #5 · callstackincubator/rozenite
This branch introduces a new Redux DevTools plugin for Rozenite, providing Redux state inspection and debugging capabilities within React Native DevTools. The plugin enables real-time state monitor...
github.com
July 29, 2025 at 5:16 PM
Redux DevTools plugin for Rozenite is nearly complete. It offers basic debugging functionality, though without time travel or action dispatch capabilities. There's an upstream issue with the package that needs to be addressed first.
github.com/callstackinc...
github.com/callstackinc...
Rozenite - a plugin framework for React Native DevTools - is now live in alpha! 🎉
What started as a hacky PoC is now something you can use in real projects.
Still lots to come: better network monitor, Redux DevTools, Re.Pack support & more 💪
What started as a hacky PoC is now something you can use in real projects.
Still lots to come: better network monitor, Redux DevTools, Re.Pack support & more 💪
July 28, 2025 at 7:20 PM
Rozenite - a plugin framework for React Native DevTools - is now live in alpha! 🎉
What started as a hacky PoC is now something you can use in real projects.
Still lots to come: better network monitor, Redux DevTools, Re.Pack support & more 💪
What started as a hacky PoC is now something you can use in real projects.
Still lots to come: better network monitor, Redux DevTools, Re.Pack support & more 💪
Big news: the React Native DevTools framework is dropping by the end of this month 🔥
The name? It's locked in and I'm so excited about it. It kicks off a whole family of tools designed to push React Native even further… but I'm not allowed to say anything else at this point 🙊
The name? It's locked in and I'm so excited about it. It kicks off a whole family of tools designed to push React Native even further… but I'm not allowed to say anything else at this point 🙊
July 16, 2025 at 2:46 PM
Big news: the React Native DevTools framework is dropping by the end of this month 🔥
The name? It's locked in and I'm so excited about it. It kicks off a whole family of tools designed to push React Native even further… but I'm not allowed to say anything else at this point 🙊
The name? It's locked in and I'm so excited about it. It kicks off a whole family of tools designed to push React Native even further… but I'm not allowed to say anything else at this point 🙊
Just found out I'll be speaking at React Advanced!
I'll be sharing my journey hacking on React Native Devtools + building a plugin framework from scratch.
If you're curious how it all came together, tune in!
The live stream is free - just register here: gitnation.com/badges/react...
I'll be sharing my journey hacking on React Native Devtools + building a plugin framework from scratch.
If you're curious how it all came together, tune in!
The live stream is free - just register here: gitnation.com/badges/react...
Check out my badge & claim your free React Advanced 2025 remote ticket!
Join 5k engineers worldwide at React Advanced 2025 and meet 50+ top speakers at Nov 27 - Dec 1, 2025
gitnation.com
July 14, 2025 at 7:20 PM
Just found out I'll be speaking at React Advanced!
I'll be sharing my journey hacking on React Native Devtools + building a plugin framework from scratch.
If you're curious how it all came together, tune in!
The live stream is free - just register here: gitnation.com/badges/react...
I'll be sharing my journey hacking on React Native Devtools + building a plugin framework from scratch.
If you're curious how it all came together, tune in!
The live stream is free - just register here: gitnation.com/badges/react...
Built a file-based router for React Native - just for fun.
It kinda works 😅
Learned a lot about Metro internals and found some cool low-level APIs along the way.
Gave a talk about it! Check it out 👇
www.youtube.com/watch?v=oQjF...
It kinda works 😅
Learned a lot about Metro internals and found some cool low-level APIs along the way.
Gave a talk about it! Check it out 👇
www.youtube.com/watch?v=oQjF...
I Built a File-Based Router for React Native by Szymon Chmal | React Universe Meetup, April 2025
YouTube video by Callstack Engineers
www.youtube.com
May 8, 2025 at 8:10 AM
Built a file-based router for React Native - just for fun.
It kinda works 😅
Learned a lot about Metro internals and found some cool low-level APIs along the way.
Gave a talk about it! Check it out 👇
www.youtube.com/watch?v=oQjF...
It kinda works 😅
Learned a lot about Metro internals and found some cool low-level APIs along the way.
Gave a talk about it! Check it out 👇
www.youtube.com/watch?v=oQjF...
Short RSC update:
✅ 'use client' and 'use server' now become proxies.
✅ Server rendering is... holding together with duct tape.
Now to bundle client components and pray React Native accepts them 🙃
✅ 'use client' and 'use server' now become proxies.
✅ Server rendering is... holding together with duct tape.
Now to bundle client components and pray React Native accepts them 🙃
April 28, 2025 at 2:19 PM
Short RSC update:
✅ 'use client' and 'use server' now become proxies.
✅ Server rendering is... holding together with duct tape.
Now to bundle client components and pray React Native accepts them 🙃
✅ 'use client' and 'use server' now become proxies.
✅ Server rendering is... holding together with duct tape.
Now to bundle client components and pray React Native accepts them 🙃
The sun’s out, the birds are singing... and I’m buried in last-minute tweaks to the playground app for today’s JavaScript Performance webinar 😅
Still time to grab a spot if you missed the announcement! 👇
streamyard.com/watch/pnM9CY...
Still time to grab a spot if you missed the announcement! 👇
streamyard.com/watch/pnM9CY...
Master JavaScript Performance in React Native: Part 2
This is Part 2 of our JavaScript optimization deep dive—a continuation of the webinar we hosted two weeks ago, based on Part 1 of Callstack’s Ultimate Guide to React Native Optimization.
Hosted by:
🎙...
streamyard.com
April 28, 2025 at 1:48 PM
The sun’s out, the birds are singing... and I’m buried in last-minute tweaks to the playground app for today’s JavaScript Performance webinar 😅
Still time to grab a spot if you missed the announcement! 👇
streamyard.com/watch/pnM9CY...
Still time to grab a spot if you missed the announcement! 👇
streamyard.com/watch/pnM9CY...
Missing memoization where it matters most?
Let’s fix that.
Join us for Part 2 of our React Native JavaScript perfomance deep dive - debounce, selectors, state shape & more.
📅 Apr 29 • 6PM CET
🎙️ @grabbou.com + me
🎟️ streamyard.com/watch/pnM9CY...
Let’s fix that.
Join us for Part 2 of our React Native JavaScript perfomance deep dive - debounce, selectors, state shape & more.
📅 Apr 29 • 6PM CET
🎙️ @grabbou.com + me
🎟️ streamyard.com/watch/pnM9CY...
April 25, 2025 at 4:04 PM
Missing memoization where it matters most?
Let’s fix that.
Join us for Part 2 of our React Native JavaScript perfomance deep dive - debounce, selectors, state shape & more.
📅 Apr 29 • 6PM CET
🎙️ @grabbou.com + me
🎟️ streamyard.com/watch/pnM9CY...
Let’s fix that.
Join us for Part 2 of our React Native JavaScript perfomance deep dive - debounce, selectors, state shape & more.
📅 Apr 29 • 6PM CET
🎙️ @grabbou.com + me
🎟️ streamyard.com/watch/pnM9CY...
Your React Native application slowed down? We are here to help you! Join our walkthrough of Callstack's 2025 Optimization Guide (Part 1). You will have the opportunity to ask questions and have them answered for free, without any hidden catches.
streamyard.com/watch/VW8Ufy...
streamyard.com/watch/VW8Ufy...
April 11, 2025 at 2:36 PM
Your React Native application slowed down? We are here to help you! Join our walkthrough of Callstack's 2025 Optimization Guide (Part 1). You will have the opportunity to ask questions and have them answered for free, without any hidden catches.
streamyard.com/watch/VW8Ufy...
streamyard.com/watch/VW8Ufy...
I'm gathering examples of situations where developers might choose popular tools or patterns without fully considering if they fit the project's needs. For instance, using SSR for dynamic dashboards where it's not really necessary. Got any ideas for similar examples? 🧐
March 10, 2025 at 7:06 PM
I'm gathering examples of situations where developers might choose popular tools or patterns without fully considering if they fit the project's needs. For instance, using SSR for dynamic dashboards where it's not really necessary. Got any ideas for similar examples? 🧐
Another hype cycle is starting. People are asking if they should learn Lynx, as it's being called a "React Native killer." It’s probably too early to say, but some influencers are already fueling the buzz for views and likes.
March 10, 2025 at 7:04 AM
Another hype cycle is starting. People are asking if they should learn Lynx, as it's being called a "React Native killer." It’s probably too early to say, but some influencers are already fueling the buzz for views and likes.
Lynx: a hit or a miss? Let's find out together. This is going to be fun 🔥
LynxJS: Fresh Take or Just a Copy-Paste?
We’re going live this Friday, March 7th at 5:30 PM CET to check out LynxJS for the first time. Join me, @grabbou.com, @matthargett.bsky.social and @chmal.it as we test it out, live code, and share our thoughts.
Where?
📺 www.youtube.com/watch?v=MCCy...
We’re going live this Friday, March 7th at 5:30 PM CET to check out LynxJS for the first time. Join me, @grabbou.com, @matthargett.bsky.social and @chmal.it as we test it out, live code, and share our thoughts.
Where?
📺 www.youtube.com/watch?v=MCCy...
LynxJS: First Impressions, Live Coding & What’s Under the Hood
YouTube video by Callstack Engineers
youtube.com
March 6, 2025 at 4:42 PM
Lynx: a hit or a miss? Let's find out together. This is going to be fun 🔥
Been exploring visual regression testing tools for React Native lately and it feels like the space is underdeveloped. 🤔 What features would your dream visual regression tool have to make you want to use it?
February 26, 2025 at 12:37 PM
Been exploring visual regression testing tools for React Native lately and it feels like the space is underdeveloped. 🤔 What features would your dream visual regression tool have to make you want to use it?