Uncaught ReferenceError: babelHelpers is not defined

[ruud]

We are trying to implement CSP in our Polymer 2 application. The suggested way is by adding crisper to our polymer build. Unfortunately, when adding this additional step we get the following error:

Uncaught ReferenceError: babelHelpers is not defined

Without crisper, all works just fine. My question is:

• to use CSP, do we need crisper?
• why does it need the babelHelpers? Or why is it not included?