enable strict mode in JavaScript

Gemfile

@@ -12,14 +12,12 @@ gem 'uglifier', '>= 1.0.3'
 # database
 gem 'pg'
 
+# use "strict mode" in JavaScript
+gem 'sprockets-strict-mode'
+
 # for building JSON
 gem 'jbuilder', '~> 1.2'
 
-# HTTP server for Rack applications for staginng and production
-# See https://github.com/bigbinary/wheel/issues/43 for why unicorn is
-# not used in development.
-gem 'unicorn', group: [:staging, :production]
-
 # for authentication
 gem 'devise', '3.2.3'
 
@@ -56,12 +54,17 @@ gem 'rails_12factor'
 # for email validation
 gem 'email_validator'
 
-# For variants support
+# for variants support
 gem 'browser'
 
-# Haml as templating engine
+# haml as templating engine
 gem 'haml-rails'
 
+# HTTP server for Rack applications for staginng and production
+# See https://github.com/bigbinary/wheel/issues/43 for why unicorn is
+# not used in development.
+gem 'unicorn', group: [:staging, :production]
+
 group :development do
 
   # application server for development

Gemfile.lock

@@ -227,6 +227,8 @@ GEM
       actionpack (>= 3.0)
       activesupport (>= 3.0)
       sprockets (>= 2.8, < 4.0)
+    sprockets-strict-mode (1.0)
+      sprockets
     thin (1.6.3)
       daemons (~> 1.0, >= 1.0.9)
       eventmachine (~> 1.0)
@@ -279,6 +281,7 @@ DEPENDENCIES
   simplecov
   spring
   sprockets-rails (~> 2.0)
+  sprockets-strict-mode
   thin
   twitter-bootstrap-rails
   uglifier (>= 1.0.3)

config/initializers/enable_strict_mode_in_javascript.rb

@@ -0,0 +1,2 @@
+# as per https://github.com/jsuder/sprockets-strict-mode
+Rails.application.assets.register_postprocessor('application/javascript', Sprockets::StrictMode)