Debugging browser-window.js

We are having great difficulties in getting our electron app to run locally on Windows. The app was made by an external contractor and while they where able to build on Windows and ship the packaged app to us, we can not get it to work with the checked-in source code.

I would like to debug the app in vscode and are able to step into our main.js file but what I would really like to see is what happens in the .loadURL() method of BrowserWindow. Unfortunately, vscode tells me that it is:

Unable to open ‘browser-window.js’: Unable to read file (Error: File not found (c:\Users\dotnet\Projects\napp\sales-app\node_modules\electron\dist\resources\electron.asar\browser\api\browser-window.js)).

I understand that an .asar file is simply concatenated files without compression. So I tried to unpack it via asar extract but this of course broke electron.

I am installing prerequisites as listed in the build instructions but I am hoping there is a simpler way to debug electron (not the electron app). I am, so far, only interested in the .js files and not the native (C++) executables.