JSON error with coffeescript & Rails asset pipeline

Question

I am using Rails 3.2.14 without issue...

I have recently renamed application.js to application.js.coffee and am now getting a JSON error.

JSON::GeneratorError

only generation of JSON objects or arrays allowed
  (in /.../app/assets/javascripts/application.js.coffee)

Even when I delete all the contents of application.js.coffee I still get the error.

When I try to view it directly (http://localhost:3000/assets/application.js), its the same issue:

throw Error("JSON::GeneratorError: only generation of JSON objects or arrays allowed\n  (in /.../app/assets/javascripts/application.js.coffee)")

I have combed my app for any potential issues but everything looks pretty standard.

Answer 1

I had a similar problem (Rails 4 asset pipeline throws "only generation of JSON objects or arrays allowed"), which had nothing to do with application.js. The multi_json gem got updated from 1.7.8 to 1.7.9, and broke my app. Any change to the cofeescript-files resulted in this "only generation of JSON objects or arrays allowed" error.

I explicitly put the multi_json gem in my Gemfile, fixed to version 1.7.8. In solved the problem for me.

Answer 2

I have the save issue not in a Rails project, but a ruby project using sprockets. I have not finally determined the problem, but it seems to be related to execjs and the Javascript runtime used.

You can try to add

gem 'therubyracer'

to your Gemfile. This installs the v8 engine, which solved the problem for me.