Exception with JSON Rendering in Rails

Json_except.rb

# I use this code to render the JSON

format.js { render :json => @courses_list.to_json( :except => [ :account_id, :default_view, :public_syllabus, :storage_quota_mb, :apply_assignment_group_weights, :calendar ] )}

# But it still give me this as result :

[
  {
    "account_id":1,
    "course_code":"Audio Mastering 101 - 0913",
    "default_view":"feed",
    "id":1,
    "name":"Audio Mastering 101",
    "start_at":"2013-09-16T00:00:00+02:00",
    "end_at":"2013-10-13T23:55:00+02:00",
    "public_syllabus":false,
    #.....
  },
  {
    "account_id":1,
    "course_code":"Sound Design 101",
    "default_view":"feed",
    "id":2,
    "name":"Sound Design 101",
    "start_at":"2013-08-06T16:55:25+02:00",
    "end_at":null,
    "public_syllabus":false,
    #.....
  }
]