Minify embedded javascripts in slim when not in development (Ruby 2+)

slim_js_minifier.rb

if !Rails.env.development? && defined? Slim::Embedded::JavaScriptEngine
  module Slim
    # Collector to extract JS from compiled templates
    class JsCollector < Interpolation 
      def call(exp)
        @collected = ''
        super(exp)
        @collected
      end

      def on_slim_interpolate(text)
        @collected << self.class.new.call(super(text))
        nil
      end

      def on_static(text)
        @collected << text
        nil
      end
    end

    # Code responsible for applying minification
    module JsMinifier
      def js_collector
        @js_collector ||= JsCollector.new
      end

      def collect_text(body)
        js_collector.call(body)
      end

      def on_slim_embedded(*args)
        ret = super(*args)
        if defined? Uglifier
          js_raw = collect_text(ret)
          js_min = Uglifier.compile(js_raw)
          ret[4] = [:static, js_min]
        end
        ret
      end
    end

    # Default JS Embed handler
    class Embedded::JavaScriptEngine
      prepend JsMinifier
    end
  end
  
end