Apparently we have no systematic collection or sampling of JS console errors. From IRC chat: @Jdforrester-WMF (Editing PM team) has not heard of any issues. @Quiddity has not either, and has asked other community engagement folks, including @Jseddon (whom we definitely should have pinged about this earlier... sorry!!!) to keep an eye out. He also checked VPT and meta:Talk:CentralNotice, with no indications of issues showing up there, either.
Thanks much, all!!