Niels Leenheer

CTO of Salonhub. Creator of https://html5test.com, writes at https://nielsleenheer.com, team @FronteersConf, Google Developers Expert, Invite me to speak at your event.

Website: https://nielsleenheer.com
Github: http://github.com/nielsleenheer
Bluesky: https://bsky.app/profile/html5test.com

Last Notes

2026-09-25 14:03:04 UTC

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And it is now the best ESC/POS and StarPRNT renderer there is. Probably even better than some printers.
But it will probably be used by just me. Or at most a handful of people.
And that is fine. I love this project.

2026-09-25 14:01:28 UTC

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I generated receipts using a dozen different open-source encoders and test suites of other rendered and compared them manually with the output of dozens of printers. Painstakingly making sure to capture every single quirk and detail...

2026-09-25 13:59:37 UTC

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The result is a renderer that exactly matches a real printer. And it does not just support the code my own projects generate…
https://cdn.masto.host/frontendsocial/media_attachments/files/117/332/027/630/942/896/original/d9cc5c1214b2cf57.png

2026-09-25 13:56:40 UTC

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And to render receipts, you need a bitmap font at specific sizes. And there wasn't yet one...
So I created a bitmap font editor... I know 🤪
https://cdn.masto.host/frontendsocial/media_attachments/files/117/332/018/563/934/383/original/952aa515f0fc45f3.png

2026-09-25 13:53:29 UTC

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But... what I really wanted is a renderer. For two reasons - some printers only support bitmaps, and I wanted to be able to print on those too.
But I also wanted to have a preview to see how a receipt rendered.
https://cdn.masto.host/frontendsocial/media_attachments/files/117/332/005/181/141/732/original/2b7594ffa4fbe5d5.png

2026-09-25 13:51:15 UTC

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From the moment I've been working on this - 15 years ago - I've always wanted to build a decoder, so that I could inspect what we actually send to the printer... every single command that it receives.
https://cdn.masto.host/frontendsocial/media_attachments/files/117/331/998/453/816/104/original/f1e63d38229214cc.png

2026-09-25 13:49:32 UTC

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And you end up with bytes. Just raw bytes that you send to the printer - also with libraries that I created...
https://cdn.masto.host/frontendsocial/media_attachments/files/117/331/994/952/382/449/original/25d7a5b2eb5cfec3.png

2026-09-25 13:48:10 UTC

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But let's rewind. You start with some JavaScript and my ReceiptPrinterEncoder library to create the actual receipt. From JavaScript, in the browser or a server. Or using Capacitor or Electron. I've build integrations for everything.
https://point-of-sale.dev
https://cdn.masto.host/frontendsocial/media_attachments/files/117/331/983/950/410/334/original/2ade201a22efcb9c.png

2026-09-25 13:44:24 UTC

And this is what I've been spending my evenings on lately. A decoder for receipt printer protocols. You can take the bytes that get send to a receipt printer and inspect the commands that are inside of it. And... actually see a render of the receipt.
Only useful for a hand full of people. And me.
https://cdn.masto.host/frontendsocial/media_attachments/files/117/331/974/010/484/223/original/d99116b7bf73ecd7.mp4

2026-09-24 17:07:04 UTC

RE: https://front-end.social/@heydon/117315437800953545
I've seen Heydon's talk a week or two ago at [@smashingconf](https://mastodon.social/@smashingconf ) and it was amazing. I just loved it so much.
So if you want to see it... come down to Dordrecht in The Netherlands... A handful of tickets are still available.
https://www.fronteersconf.org
#note1s0w…5j9h

2026-04-05 10:22:29 UTC

Take a Joy-Con and connect it with WebHID, draw a picture in the air and capture it with the sensors. Create an SVG path and insert in the DOM. Apply CSS styling. Sample the DOM and use WebUSB to convert to ILDA and send it to a laser projector.
I created the worlds most complicated laserpointer…
https://cdn.masto.host/frontendsocial/media_attachments/files/116/351/601/206/686/862/original/86dd54ff76a93137.mp4

2026-03-27 15:18:10 UTC

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Want to know how I created this?
Check my blog post with an explanation of the math, the techniques I used and the problems I ran into.
https://nielsleenheer.com/articles/2026/css-is-doomed-rendering-doom-in-3d-with-css/

2026-03-27 15:16:48 UTC

CSS is DOOMed!
I've build DOOM in CSS and every wall, floor, barrel, and imp is a div, positioned in 3D space using CSS transforms.
https://cssdoom.wtf
Try it out! But... not every browser can handle it. This is taking the browser to its limit. Chrome has some issues. Safari too. Bugs will be filed.
https://cdn.masto.host/frontendsocial/media_attachments/files/116/301/800/628/808/007/original/da39c38dd8b4a407.jpg