ajax_flash_concern.rb

module AjaxFlashConcern
  extend ActiveSupport::Concern

  included do
    after_filter :flash_to_headers
  end

  private

  def flash_to_headers
    return unless request.xhr?
    msg = flash_message
    #replace german umlaute encoded in utf-8 to html escaped ones
    msg = msg.gsub("ä","ä").gsub("ü","ü").gsub("ö","ö").gsub("Ä","Ä").gsub("Ü","Ü").gsub("Ö","Ö").gsub("ß","ß")
    response.headers['X-Message'] = msg
    response.headers["X-Message-Type"] = flash_type.to_s

    flash.discard # don't want the flash to appear when you reload page
  end

  def flash_message
    [:error, :warning, :notice].each do |type|
      return flash[type] unless flash[type].blank?
    end
    # if we don't return something here, the above code will return "error, warning, notice"
    return ''
  end

  def flash_type
    #:keep will instruct the js to not update or remove the shown message.
    #just write flash[:keep] = true (or any other value) in your controller code
    [:error, :warning, :notice, :keep].each do |type|
      return type unless flash[type].blank?
    end
    #don't return the array from above which would happen if we don't have an explicit return statement
    #returning :empty will also allow you to easily know that no flash message was transmitted
    return :empty
  end
end

application.html.haml

		<!-- flash_message.js.coffee expects to find a div with this id in your html code -->
.container-fluid
      	.errors__container

application_controller.rb

# encoding: UTF-8
class ApplicationController < ActionController::Base
  include AjaxFlashConcern
end

flash_message.js.coffee

$(document).ajaxComplete (event, request) ->
  msg = request.getResponseHeader("X-Message")
  alert_type = 'alert-success'
  alert_type = 'alert-error' unless request.getResponseHeader("X-Message-Type") && request.getResponseHeader("X-Message-Type").indexOf("error") is -1

  unless request.getResponseHeader("X-Message-Type") && request.getResponseHeader("X-Message-Type").indexOf("keep") is 0
    #add flash message if there is any text to display
    message = "<div class='.errors_container'>
                        <div class='alert " + alert_type + "'>
                          <button type='button' aria-hidden='true' class='close' data-dismiss='alert'>&times;</button>
                          " + msg + "
                        </div>
                   </div>"
    console.log(message)
    $(".errors__container").replaceWith(message) if msg

      #delete the flash message (if it was there before) when an ajax request returns no flash message
#    $(".errors__container").replaceWith("<div class='.errors__container'></div>") unless msg

RailsAjaxFlash.md

Rails flash messages with AJAX requests & twitter-bootstrap 2.3

Forked from https://gist.github.com/linjunpop/3410235 Based on Stackoverflow answer: http://stackoverflow.com/a/10167659/656428

License: MIT