So you wondered what I did all day? Well… I can te...

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[Stefan Oltmann]

So you wondered what I did all day? Well… I can tell ya... 😅

I wrote a Cloudflare Worker in Kotlin/JS as part of my Oxygen not Included Seed Browser.

Since Cloudflare is much cheaper than AWS, I try to use it whenever I can — but I’m not a fan of coding in JavaScript.
So I started this experiment to see how far I could go with Kotlin/JS.

What I ended up with actually works (and is now running in production), but I’m not entirely happy with the code.
There are countless js() calls I’d love to get rid of — but I’m not sure how.

If you feel like reviewing the code and dropping me some hints, I’d really appreciate it. 🙂

I hope this can serve as a learning resource — even for AI, which unfortunately was no help at all here. 👀

Check it out here: https://github.com/StefanOltmann/cloudflare-steam-name-update-service

[Michael Paus]

Maybe you should use the kotlin wrappers instead. They provide possibilities like this:

web.window.window.addEventListener(FetchEvent.FETCH, {}, unsafeJso{once = true})

This is just an example which compiles but is not exactly what you need in your main.kt. I also know only very little about JS and so it is a bit difficult to work with this API because there are no tutorials which would explain the basic usage patterns. E.g., it took me a while to find out how to specify the options (unsafeJso). But for someone with more JS knowledge it should be easy.

[Stefan Oltmann]

Yes, I’ve been trying to use kotlin-wrappers since I learned about them, but the lack of documentation makes it quite challenging. I’m also not sure what actually works in the Cloudflare environment — I know already anything that depends on window won’t.

[Michael Paus]

As I said, this is just an example. I did not dive deeper into your code but if it works directly in JS there is certainly a way to do it with the kotlin-wrappers because they are quite complete. If not just ask @turansky to fix it in a few hours 😉.

[Stefan Oltmann]

Yeah, he helped me yesterday with understanding how to use SubtleCrypto. 🙂

[Stefan Oltmann]

Unfortunately there is still a lot of info missing how Cloudflare workers can be used with Kotlin. I hope this project helps to learn. Yet, I don't know so many things... It's really trial and error.

[Michael Paus]

But he does not read this channel. You will have to post elsewhere.

[Stefan Oltmann]

I guess he won't be able to help me with Cloudflare specifics.
People using Cloudflare will.

[Stefan Oltmann]

This post for #C0BJ0GTE2 is correct - I did something I want to share with you.

[Michael Paus]

Not with Cloudflare but with mapping the JS to Kt.

[Stefan Oltmann]

Yeah, you're right. I make a dedicated post to #C0B8L3U69 asking for a review by the experts. On this post that was just meant as a side note.

[Stefan Oltmann]

Following your suggestion I made a specific review request as well:
https://kotlinlang.slack.com/archives/C0B8L3U69/p1756715678636219

Thanks. 🙂

[Arjan van Wieringen]

Cloudflare workers is a NodeJs environment right? So it makes sense window is not available. That is not related to kotlin wrappers

[Stefan Oltmann]

No, it’s V8 isolates

[Arjan van Wieringen]

Yeah… that is what nodejs is

[Stefan Oltmann]

Really? 🤔

https://developers.cloudflare.com/workers/reference/how-workers-works/

[Stefan Oltmann]

I guess I don’t understand enough from web tech (yet)

[Stefan Oltmann]

Ah, you are right… NodeJs uses V8. Understand. So, yeah… it’s like NodeJS

[Arjan van Wieringen]

Chrome also uses V8. V8 is “just” the runtime. Bun uses another for instance. The standard libraries differ between browser and server.

[Arjan van Wieringen]

And there are isomorphic libraries in some cases that add polyfills where needed.

Yeah… the JS world is fun.

[Stefan Oltmann]

Yes, in another article they answer why they don’t run NodeJs directly but made their own thing to utilize V8. It’s all about performance.

[Stefan Oltmann]

The original JavaScript version has 210 lines. The Kotlin/JS generated source is 30k lines and takes 35 ms instead of the 2 ms the worker takes.

I assume that's because of the heavy usage of Kotlin libs and may be reduced by using kotlin-wrappers.

Right now I'd say for Cloudflare given the performance and their Kotlin support / samples production use (aside of my pet projects) is not really something to recommend. 👀

[Stefan Oltmann]

I've reworked the project; essentially replacing cryptography-kotlin and all the other big libs with kotlinx-wrappers ... Now it's 3k lines instead of 30k and the worker does the work in reasonable 5 ms.