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Jason Williams

@jason-williams.co.uk
1.4K followers 199 following 31 posts

JavaScript Infrastructure & Tooling @Bloomberg @TC39, creator of Boa (JS Engine)

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Jason Williams @jason-williams.co.uk · 01/05/2026
Excited about this, we've been working on the upcoming Container Timing API. Want to learn more? Take a read of the blog post below, put together with @tunetheweb.com and @jdapena.bsky.social. Feedback is very welcome. Try it out and help us shape this API! [This feature is Mozilla Approved]
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Henri Helvetica 🧑🏾‍🚀🇭🇹 @henrihelvetica.bsky.social · 15/04/2026
Had a delightful session today. A great conversation was had w/ @jdapena.bsky.social of @igalia.com about the work being done w/ container timing in Chrome. Both @jason-williams.co.uk + @andydavies.me got mentions. 🙃 This should be published soon. Thx to all who joined in!
Two persons during an online interview smiling. SPD stream number 030. One is wearing an orange toque black glasses button up shirt in front of a microphone with a pink foam. The other wearing a headset and a navy blue sweater.
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Jason Williams @jason-williams.co.uk · 30/03/2026
I will be speaking at #JSNation about Boa: A JavaScript engine in Rust. The Journey, what it taught me and how it works. Check out my #JSNation badge: gitnation.com/badges/jsnat.... Register via the badge and watch the stream for FREE! See you on June 11 & 15.
gitnation.com
Check out my badge & claim your free JSNation 2026 remote ticket!
Join 10k engineers worldwide at JSNation 2026 and meet 50 top speakers at June 11 - 15, 2026
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Rob Palmer @robpalmer.bsky.social · 26/03/2026
Container Timing is a new web performance metric to measure when an area of the screen gets painted ⏲️ @jdapena.bsky.social and @jason-williams.co.uk have been working on it for the last couple of years. It's in Chromium, behind a flag. Hopefully coming to an origin-trial near you soon!
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Jason Williams @jason-williams.co.uk · 18/03/2026
Thanks all for watching both in person and on the @londonwebstandards.org site! It was a pleasure to present at State Of The Browser 2026 (despite going over time!), hope to be back again next year #sotb
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London Web Standards @londonwebstandards.org · 18/03/2026
The recording of @jason-williams.co.uk talk ‘Temporal: It’s about time!’ is now available to watch online! 2026.stateofthebrowser.com/speaker/jaso... And Temporal has reached Stage 4: www.igalia.com/2026/03/13/T...
A banner that reads: Temporal: It's about time!, Jason Williams, 2026 State of the Browser and it features a colourful geometric graphic in the background.
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Stuart Langridge @sil.kryogenix.org · 18/03/2026
good talk from @jason-williams.co.uk at #SotB26 2026.stateofthebrowser.com/speaker/jaso... about Temporal, the thing that will sweep Date.parse() out of our horrified memories and into the dustbin of history (finally, hooray)
2026.stateofthebrowser.com
Jason Williams | State of the Browser
Jason Williams is a senior software engineer on Bloomberg’s performance team and the creator of the Boa JavaScript engine, an experimental Rust-based engine for the web. With two decades of experience...
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Jason Williams @jason-williams.co.uk · 11/03/2026
Temporal is now Stage 4 at TC39 🎂🎂🎂 Thanks to all the other champions of JavaScript's new date-time API. It has been a wild ride over many years! I wrote a blog post explaining how we got here 📜 bloomberg.github.io/js-blog/post...
Code example showing the usage of Temporal.ZoneddateTime

```js
// London DST starts: 2026-03-29 01:00 -> 02:00
const zdt = Temporal.ZonedDateTime.from(
  "2026-03-29T00:30:00+00:00[Europe/London]",
);

console.log(zdt.toString());
// → "2026-03-29T00:30:00+00:00[Europe/London]"

const plus1h = zdt.add({ hours: 1 });

console.log(plus1h.toString());
// "2026-03-29T02:30:00+01:00[Europe/London]" (01:30 doesn't exist)
```
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Jason Williams @jason-williams.co.uk · 01/03/2026
Wow, was not expecting the mention from my talk to have that much of an effect, sorry @samwho.dev 😂, yes this was from #SotB26, it’s a good resource!
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Oliver Turner @oliverturner.cloud · 28/02/2026
@jason-williams.co.uk LOVED the talk, congrats on absolutely smashing it despite the residue of illness 🙌 Hadn’t realised that the Promise method you were referring to was allSettled… thanks so much for delivering my favourite addition 🫶
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Rob Palmer @robpalmer.bsky.social · 25/02/2026
Container Timing - a new W3C performance metric - has migrated from Bloomberg to the WICG Github org 🎉 @jason-williams.co.uk made the Bloomberg Terminal use this web metric to measure human-perceived time to start apps. We've found it more useful than existing metrics. github.com/WICG/contain...
github.com
GitHub - WICG/container-timing: Container Timing
Container Timing. Contribute to WICG/container-timing development by creating an account on GitHub.
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Rob Palmer @robpalmer.bsky.social · 13/01/2026
By many metrics the new Temporal date-time API is the single biggest change to JS ever 🔥 Like Kiesel, V8 chose to reuse Boa's open source Rust-based temporal_rs by @jason-williams.co.uk from TechAtBloomberg, Kevin Ness & Manish 👍 boajs.dev/blog/2025/09...
boajs.dev
Temporal_rs is here! The datetime library powering Temporal in Boa, Kiesel, and V8 | Boa JS
Temporal_rs is here! The datetime library powering Temporal in Boa, Kiesel, and V8
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Rob Palmer @robpalmer.bsky.social · 09/01/2026
State of the Browser 2026 🎉 28th Feb in London 🇬🇧 @jason-williams.co.uk will present "It's about time" discussing the new JavaScript Temporal API ⌚
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Dave Letorey @letorey.co.uk · 07/01/2026
I built a countdown to State of the Browser using #TemporalAPI codepen.io/CodeRedDigit... Come see @jason-williams.co.uk talk about it
codepen.io
Time until State of the Browser 2026
...
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Jason Williams @jason-williams.co.uk · 19/12/2025
Woo! Cannot wait to speak at State Of The Browser 2026. Looking forward to meeting other people in this space too, see you next year!
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Mary Branscombe @marypcbuk.bsky.social · 12/12/2025
I've been writing about Temporal (what @b.trl.sn calls 'the fix for our broken date object' which is so bad @samwho.dev made a quiz) for a long time and this time, maybe this time, it's really time for temporal @jason-williams.co.uk tells me, which will make @bkardell.com and many developers happy
thenewstack.io
ES2026 Solves JavaScript Headaches With Dates, Math and Modules
With ECMAScript 2026, JavaScript will get more precise about sums, errors, international dates and times — and it may finally be time for Temporal.
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Rob Palmer @robpalmer.bsky.social · 09/12/2025
ECMAScript excitement 😉 A highly comprehensive article on what will (and might!) land in ES2026 by @marypcbuk.bsky.social 🎉 Includes coverage on Temporal by Boa creator @jason-williams.co.uk who leads the Rust-based temporal_rs library, as used by Google's V8 engine, amongst others.
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Jason Williams @jason-williams.co.uk · 15/11/2025
Fancy seeing @boajs.dev trending on hacker news! news.ycombinator.com/item?id=4583...
news.ycombinator.com
Boa: A standard-conforming embeddable JavaScript engine written in Rust | Hacker News
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Rob Palmer @robpalmer.bsky.social · 04/11/2025
ECMAScript excitement 😉 Congrats to @manishearth.bsky.social on unflagging TC39 Stage 3 Temporal in V8 today. Heading for Chrome 144 🎉 By many metrics this new date-time API is the single biggest change to JS ever 🔥 V8 uses Boa's temporal_rs by @jason-williams.co.uk Kevin Ness & Manish 👍
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Jason Williams @jason-williams.co.uk · 31/10/2025
Thanks @mmocny.com for the container timing shoutout and stealing my low effort diagram 😂 Great talk @ #perfnow
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Boa @boajs.dev · 23/10/2025
Boa v0.21 has been released! Plenty of new features, builtins and performance improvements. Blog post with details boajs.dev/blog/2025/10... Discussions: Lobste.rs: lobste.rs/s/upi3xa/boa... news.ycombinator.com/item?id=4567... www.reddit.com/r/rust/comme...
boajs.dev
Boa release v0.21 | Boa JS
Boa release v0.21
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Jason Williams @jason-williams.co.uk · 24/09/2025
This is huge, Temporal is on its way, its been a long effort and great to see collaboration on a centralized Rust library including V8 who have never integrated Rust before now! Shout out to everyone who has been involved. Much more info in the blog post!
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Nicholas Nethercote @nnethercote.bsky.social · 18/07/2025
New blog post: I am a Rust compiler engineer looking for a new job nnethercote.github.io/2025/07/18/l...
nnethercote.github.io
I am a Rust compiler engineer looking for a new job
For the past 3.75 years I have been fortunate to work on Futurewei’s Rust team, where I had enormous freedom to “make Rust better” however I see fit. It has been the highlight of my career and I am gr...
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Jason Williams @jason-williams.co.uk · 17/07/2025
Hey thanks for the inclusion @infrequently.org, I feel honoured!
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Jason Williams @jason-williams.co.uk · 16/07/2025
I’ve added support for the DAP “startDebugging” request in the Helix Editor. This means you can now debug JavaScript/TypeScript! It has been released in v25.07 helix-editor.com/news/release... PR: github.com/helix-editor...
helix-editor.com
Release 25.07 Highlights | Helix
A post-modern modal text editor.
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Rob Palmer @robpalmer.bsky.social · 22/06/2025
Boa's temporal_js may turn out to be one of the most widely used implementations of the TC39 Stage 3 Temporal API 👍 An independent open source project having impact on the whole JS ecosystem. The Boa community has come along way since it was started by @jason-williams.co.uk seven years ago.
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Rachel Andrew @rachelandrew.co.uk · 13/02/2025
Interop 2025 launched today! Some really exciting features set to become part of Baseline this year.
web.dev
Interop 2025: another year of web platform improvements  |  Blog  |  web.dev
Discover the features included in Interop 2025.
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Jason Williams @jason-williams.co.uk · 30/01/2025
I’ve been helping (alongside others) to Champion Temporal for around 6 years now, it’s great to see it approaching the finish line. The responses have been positive. Great work @joshcena.com and @meyerweb.com on the MDN documentation, momentous effort. Also props to the main man @ptomato.name
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Jason Williams @jason-williams.co.uk · 24/01/2025
Myself and @pcwilliams.net continue to be humbled by the response we had at @perfnow.bsky.social. Our talk “Bloomberg Becomes Browser” has been published! You can watch it here: youtu.be/y1MCLZm8yAY?...
youtu.be
Bloomberg Becomes Browser | Jason Williams & Paul Williams | performance.now() 2024
YouTube video by Web Conferences Amsterdam
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Jason Williams @jason-williams.co.uk · 14/12/2024
Fantastic to see @boajs.dev at the top of JS Weekly! Nice snake illustration too. There’s some good changes in this release and more coming up for 2025. “This is no toy engine” - javascriptweekly.com/issues/716 CC @cooperx86.bsky.social
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Boa @boajs.dev · 05/12/2024
We have released v0.20! This release includes more features, runtime additions, performance optimizations and more. boajs.dev/blog/2024/12... CC @thisweekinrust.bsky.social
boajs.dev
Boa release v0.20 | Boa JS
Boa release v0.20
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Boa @boajs.dev · 25/11/2024
Hello World!
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WebPerfWG @webperfwg.org · 22/11/2024
In our meeting yesterday, we decided to adopt Element Timing (and the followup Container Timing work) into the working group. CfC coming up!! We also discussed some upcoming improvements to the crash reporting API (still in incubation). Minutes: w3c.github.io/web-performa...
w3c.github.io
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Jason Williams @jason-williams.co.uk · 22/11/2024
Well that's made my day, jQuery was one of the first open source projects I ever contributed to (~2010!) 👋 @johnresig.com
John Resig followed you
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Jason Williams @jason-williams.co.uk · 16/11/2024
Thanks to everyone at @perfnow.bsky.social for making us feel welcome and putting on a good conference. Really enjoyed meeting you all!
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Björn Peter @spielzeugpferd.bsky.social · 15/11/2024
Crazy refreshing and insightful talk by @jasew.bsky.social & @pcwilliams.bsky.social at #perfNow! This could have continued for another hour only talking about the Container Timing API alone for my taste. Brilliant!
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Paul Williams @pcwilliams.net · 15/11/2024
Today @jasew.bsky.social and I tell the story of how our team embedded web technology to give us the best combination of real-time data and rich UI for the #BloombergTerminal. It is an honour to speak at @perfnow.bsky.social. The #PerfNow team have been so welcoming. perfnow.nl/speakers#paulw
A view of the empty chairs set up in readiness for the Performance.Now conference in Zuiderkerk in Amsterdam, with the room beautifully lit in yellow and purple lighting.
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Rob Palmer @robpalmer.bsky.social · 13/11/2024
The @perfnow.bsky.social conference begins tomorrow in Amsterdam. It is going to be great 👍 For the first time @pcwilliams.bsky.social & @jasew.bsky.social will share the story of how the Bloomberg Terminal uses web tech & what this means for the wider web ecosystem 🎉 If you see us, come say hi 👋
Bloomberg Becomes Browser
Over the years, the Bloomberg Terminal has evolved from one of the first computer-based desktop products running on custom hardware, through completely proprietary software running on Windows, to fully adopting the embedded web browser tech stack for the UI, and JavaScript/TypeScript for applications and infrastructure services.

This talk will cover our approach to making Chromium and the V8 JavaScript engine the central core of the Bloomberg Terminal, and how we have been able to understand its architecture and performance characteristics in order to deliver the kind of near-real-time responsive UI the Financial Sector demands.
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Jason Williams @jason-williams.co.uk · 12/11/2024
Hello World!
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