Client side error seen on https://en.m.wikipedia.beta.wmflabs.org/wiki/Plantilla:Cita_web
Occurs on page load. At time of writing cannot see any noticeable issues in the UI, but we should assume that they may exist.
Likely related to recent changes T191532.
To be confirmed: I suspect this might be an unbreak now. At the very minimum this is likely to be break the availability of page issues. We may need a SWAT deploy to fix.