Damn... that's honestly a shocking thing so say, if only for the fact that you can run in JS other languages. But even then, if you could "only" run JS it gives you access to a high level language but also all kind of inputs, from a keyboard and mouse, obviously, all the way to MIDI, hand tracking in WebXR, etc and all kind of outputs, e.g. screen, obviously, but also 6DoF XR, but you also get low level access to actual hardware. Totally anecdotal but I was precisely in my other browser window accessing my XR headset via adb via ... JavaScript in the browser, thanks to WebUSB. You can also run parallel computations via shaders but also WebGPU. The amount of things you can do is really mind blowing. You mind not like the syntax or some decision about the language itself but that somehow it's not interesting to have access to all that and more from any browser window is just surprising to me.
Last but not least, all that is done with 0 installation. You start a device, open the browser window, open the console and voila, you get a development environment instantly.
I just find it incredible.