Browsers limit the ability for these platforms to use raw sockets, there simply is no API for it. The best that can be done /today/ is to use WebSockets, which are not the same thing and can't be used for HTTP requests without the server expecting a WebSocket connection:

https://github.com/emscripten-core/emscripten/issues/5196#is...

Sure, sorry if it wasn't clear from my question, it wasn't specifically about urllib3, but I meant if there are plans that browsers will make such an API available or if this is something that will never become real.

I doubt browsers would allow this, though gamedevs have wanted it for decades now. Particularly UDP.

isn't the udp problem fixed with http3 unreliable webtransport?

Is it? That would be cool. Under the hood is it actual udp?

HTTP3 uses QUIC, it's not "pure" UDP, but it's a protocol based on it

https://en.wikipedia.org/wiki/QUIC

its udp with encryption and congestion control, but the aspects that gamedevs like about udp, low latency and out of order delivery without head of line blocking are features

https://developer.chrome.com/docs/capabilities/web-apis/webt...