[c0nsumer]

At least on Windows 10 for the last few years, the JS is not executed in your browser. There is specifically an isolated, limited environment called pacjsworker.exe that executes PAC files and does not support nearly the same amount of JS needed by a brower. Check this out for a list of the functions in a PAC file: http://findproxyforurl.com/pac-functions/

WinHTTP then uses this to determine if the traffic should be routed through a proxy or not.

It is not, or at least is not now, jscript.dll as the article mentions.