You'll need the app.
https://www.construct.net/en/forum/construct-3/general-discussion-7/construct-nw-js-desktop-app-131317
Specifically the Remote Preview for Nwjs
Hah Thank you newt I tested and it worked, so the browser version doesn't work with Nw.js I got it now.
There is still one problem though:
Nw.js can check if the file exists but it cannot write to a file, do you know if this is allowed?
This is my Events: