Having unpinned Ruby2JS, I found that board/agenda no longer worked. This turned out to be due to Ruby2JS generating a syntax error for events,js.rb. This seems to have emerged in v4.0.0.
The symptom is a line of the form: Events.broadcast(function(, ) { which is a syntax error. This is caused by the source line: Events.broadcast json.reporter.merge(type: :reporter) This error only seems to occur when eslevel: 5 is set. The Gemfile for board/agenda has been reverted to Ruby2JS v3.6.1 and the app now works. Sebb