ExecJS::RuntimeError with rails, how get details of error?

Question

I use rails 6 app with execJS, Sass and coffeeScript.

There is an error in my coffee code, but I don't have information to find where...

there is just an exception like this :

ExecJS::RuntimeError in Posts#index

SyntaxError: [stdin]:42:5: unexpected <

how debug ? how get more trace ?