This uses JavaScript, so it doesn't need to be sneaky about being a scale. It works offline as well, if you add it to your home screen from Safari.
Unfortunately, I can't hide the Safari UI when opening it from the home screen because for some reason the Touch.force api isn't working if I do that.
Obviously, like all the other apps, you need something like a spoon to put your items on. Small fruit and vegetables can be placed directly on the screen.
Reddit:
https://redd.it/3w2rkt (/r/iPhone)
https://redd.it/3w31a2 (/r/Apple)
based on https://github.com/freinbichler/3d-touch
Try it out at http://pltarun.github.io/scale/