Hi,
I'm having the same issue in one of my plone sites.
What conten type are you trying to edit?
I get the same javascript error when editing an Event after intalling collective.venue.
Strange thing: in another computer, the same buildout, with the same packages installed, doesn't give this error.
Versions:
Plone 5.1rc2 (5109)
CMF 2.2.12
Zope 2.13.26
Python 2.7.14