CleanEcoTemplate for Sprockets in Rails app

clean_eco_template.rb

# Put this file in lib/

require 'sprockets/eco_template'

class CleanEcoTemplate < Sprockets::EcoTemplate
  FROM = "  (function() {"
  TO = "}).call(__obj);"

  def evaluate(scope, locals, &block)
    content = Eco.compile(data)
    from = content.index(FROM)
    to = content.rindex(TO)
    content = content[from...to] + TO
    <<-JS
function(__obj) {
  if (!__obj) __obj = {};
  var __helpers = window.ecoHelpers;
  var __out = [];
  var __sanitize = __helpers.sanitize;
  var __capture = __helpers.captureFor(__obj, __out);
  var __rememberSafe = __obj.safe;
  var __rememberEscape = __obj.escape;
  __obj.safe = __helpers.safe;
  __obj.escape = __helpers.escape;
#{content}
  __obj.safe = __rememberSafe;
  __obj.escape = __rememberEscape;
  return __out.join('');
};
      JS
  end
end

eco-helpers.js

# Must include eco-helpers.js before eco files

(function(global) {
  var ecoHelpers = {
    sanitize: function(value) {
      if (value && value.ecoSafe) {
        return value;
      } else if (typeof value !== 'undefined' && value != null) {
        return ecoHelpers.escape(value);
      } else {
        return '';
      }
    },

    safe: function(value) {
      if (value && value.ecoSafe) {
        return value;
      } else {
        if (!(typeof value !== 'undefined' && value != null)) value = '';
        var result = new String(value);
        result.ecoSafe = true;
        return result;
      }
    },

    escape: function(value) {
      return ('' + value)
        .replace(/&/g, '&')
        .replace(/</g, '&lt;')
        .replace(/>/g, '&gt;')
        .replace(/"/g, '&quot;');
    },

    captureFor: function(obj, out) {
      return (function(callback) {
        var length = out.length;
        callback.call(obj);
        return ecoHelpers.safe(out.splice(length, out.length - length).join(''));
      });
    }
  };

  global.ecoHelpers = ecoHelpers;
})(window);

eco_template.rb

# Put this file in config/initializers

require 'clean_eco_template'

Rails.application.assets.register_engine '.eco', CleanEcoTemplate