I don't know if it's because of the Eval or something else, but even the example from the docs fails and the error is always the same:
$(eval const api = $(urlfetch json https://en.wikipedia.org/w/api.php?format=json&action=opensearch&search=$(querystring)); api.error || !api[1][0] ? 'Please add a query to the search' : ${api[1][0]} - ${api[3][0]})Right-hand side of 'instanceof' is not an object
On the other hand, the HTTP command from thread #16377 works (sorry I can't link yet).