Presumably you could use
3128. Does anything useful get written to the console window in settings?
If you're interested in how it works I believe it is simply: https://github.com/espruino/EspruinoTools/blob/gh-pages/core/utils.js#L363
Having said that, the easiest solution might just be to use Offline mode - also in settings. Just follow the instructions there - you can download a zip using your browser which will have a network connection, then upload it via the IDE.
I am trying to use the "native" Espruino IDE in a company network with no direct access to the internet.
My notebook is running a HTTP proxy called cntlm on port 3128.
When transferring code from the IDE to the device, the "required" modules cannot be fetched from the internet.
In Settings -> Communications I can "Enable Proxy",
but what exactly do I have to enter in "Proxy URL" and "Proxy Port" ?
I tried different variations but none of them worked.