This looks like out of scope for TE, hence adding the respective label for it to  triage further.

This should not happen. Adding component Internals > Network since proxy lookup is done there. If someone has a proxy and windows box handy, I would appreciate attempts to reproduce.

Step 2 says "execute a window.fetch request from any webpage console". Does that mean the DevTools console? If so it would be lower priority.

In my attempts, I did it in Electron 1.4.15 from the webpage, and from the console.
In Google Chrome, I have tested it only from the console.

All of that on Windows 7, I haven't tried macOS.

I may find some time to reproduce this week-end.

I have found a very dirty workaround for my use-case: I enforce the use of the fetch polyfill from github which is built on top of XHR, and it works fine.

The expectation isn't that window.fetch() use the system proxy settings... The expectation is that window.fetch() use your profile's proxy settings (which may or may not be the system proxy settings).

I tested on Mac Chrome and this works as expected.

Sounds like in your testing electron and/or Chrome are not configured to use the system proxy settings

I'm not sure I quite understand what you meant, so let me rephrase and tell me if I'm wrong:

I have tested on a VM with Windows 7 to configure a system-wide proxy setting (and no other connection was available). Google Chrome 56.0.2924.87 uses it on every request, except when it's a window.fetch (only tested in web console). However when I use jQuery to make a standard Ajax request (built on XHR) it uses the proxy settings (only tested in a web console). I believe the profile's proxy settings was well configurated.

In electron, the proxy settings are working in every other requests as well.

Is the proxy configuration of fetch different from other kinds of request? That's the only conclusion I can draw from your latest answer, and I believe it's not the case.

Also, you've tested on OSX an issue I reported on Windows. I don't believe it's the best way of reproducing.

window.fetch() should be using the same proxy settings as other requests from that page (like XHR).

I suspect there may have been an issue in your repro case. Can you provide an HTML page with your repro case, and explanation of how you are determining if a request went through proxy or not?

You may also find it useful to search for the URLs you are fetching on: chrome://net-internals/#events
That can tell you what proxy was ultimately used for the request.

Also for your system proxy settings, I suggest setting a single proxy, rather than say a PAC script which has dynamic behaviors depending on the host/path.

I will reproduce this tomorrow, but in my previous tests, I used the debug page you indicated: chrome://net-internals/#events and no proxy was used, other connections had multiple requests such as PROXY_CONNECTION if I recall correctly.