Visit https://en.m.wikipedia.org/wiki/Dog?mobileaction=beta#/categories
Note the infinite spinner.
This is broken because the categories feature makes an API request to https://en.m.wikipedia.org/w/api.php?action=query&format=json&prop=categories&titles=Dog&clprop=hidden&cllimit=50 which returns an object
IT needs to pass formatversion=2 to be able to use forEach