kramdown-rails: Use Kramdown (Markdown) in Rails 4

application_helper.rb

# app/helpers/application_helper.rb

module ApplicationHelper
  def markdown(source)
    Kramdown::Document.new(source).to_html.html_safe
  end
end

Gemfile

# Gemfile

gem 'kramdown'

kramdown.rb

# config/initializers/kramdown.rb

module Kramdown
  module Converter
    class Html
      include ActionView::Helpers::AssetTagHelper

      def convert_img(el, indent)
        attrs = el.attr.dup
        link = attrs.delete 'src'
        image_tag ActionController::Base.helpers.asset_path(link), attrs
      end
    end
  end
end

markdown_handler.rb

# config/initializers/markdown_handler.rb
 
module MarkdownHandler
  def self.erb
    @erb ||= ActionView::Template.registered_template_handler(:erb)
  end
 
  def self.call(template)
    compiled_source = erb.call(template)
    "Kramdown::Document.new(begin;#{compiled_source};end, auto_ids: false).to_html.html_safe"
  end
end
 
ActionView::Template.register_template_handler :md, MarkdownHandler
ActionView::Template.register_template_handler :markdown, MarkdownHandler