Gets the Rails flash object working with page cacheing.
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CacheableFlash Build Status


This plugin enables greater levels of page caching by rendering flash messages from a cookie using JavaScript, instead of in your Rails view template. Flash contents are converted to JSON and placed in a cookie by an after_filter in a controller or a Rack middleware in your application.

Installation as gem

gem 'cacheable_flash' # added to your Gemfile
$ bundle install


Without asset pipeline, or pre-Rails 3.1:

First copy the JS assets into your app:

rails generate cacheable_flash:install

CacheableFlash adds its javascript dependencies as a Rails 3 javascript 'expansion', which are only used if you are NOT using the asset pipeline (apparently?).

So if you have config.assets.enabled = false in application.rb then in your layout:

javascript_include_tag :cacheable_flash

Otherwise, in your layout, just source them like normal:

javascript_include_tag 'flash', 'js.cookie'

With asset pipeline (requires Rails 3.1)

The asset pipeline should have access to the assets in this gem via your app/assets/javascripts/application.js:

//= require flash
//= require js.cookie

Mailing List

Bug/Feature Tracker


Please help document!

Usage as an around filter

To use as an around filter, include the CacheableFlash module in your controller. It's all or none on the actions in your controller, so you can't mix JS and HTML display of your flash message in a controller. No other modifications to the controller are needed. You will need to add divs and some javascript to your view or layout templates to render the flash in the browser.

Note that the cookie holding the flash messages is removed as the page is displayed, so a refresh will clear the flash message (just as happens normally).

Example Controller

class MyController < ActionController::Base
  include CacheableFlash
  # ...

Usage as a Rack middleware (requires Rails 3)

To use as a Rack Middleware, swap the Rails flash middleware with the Cacheable flash middleware. Use this method if you set flash messages inside a rescue_from block:

rescue_from CanCan::AccessDenied do |exception|
  redirect_to root_url, :alert => exception.message

In your application.rb:

# Swap the ActionDispatch::Flash middleware with the CacheableFlash one
config.middleware.swap ActionDispatch::Flash, CacheableFlash::Middleware

Example Template Markup

<div id="error_div_id" class="flash flash_error"></div>
<div id="notice_div_id" class="flash flash_notice"></div>
<script type="text/javascript">
  Flash.writeDataTo('error', $('#error_div_id'));
  Flash.writeDataTo('notice', $('#notice_div_id'));

Security warning

The gem is susceptible to reflected XSS attack. Make sure no non-alphanumerical user-generated content is stored inside flash messages (html or plain text).


You can test your flash cookies by making assertions on the json of the “flash” cookie. Cacheable Flash provides test helpers which includes the flash_cookie method.

Test::Unit Example

require "cacheable_flash/test_helpers"

class TestController < ActionController::Base
  def index
    flash["notice"] = "In index"

class ControllerTest < Test::Unit::TestCase
  include CacheableFlash::TestHelpers

  def setup
    @controller =
    @request =
    @response =

  def test_cacheable_flash_action
    get :index
    assert_equal "In index", flash_cookie["notice"]

Rspec Example

require "cacheable_flash/test_helpers"

class TestController < ActionController::Base
  def index
    flash["notice"] = "In index"

describe TestController, "#index" do
  include CacheableFlash::TestHelpers

  it "writes to the flash cookie" do
    get :index
    flash_cookie["notice"].should == "In index"

Contributing to cacheable-flash

  1. Fork it

  2. Create your feature branch (`git checkout -b my-new-feature`)

  3. Commit your changes (`git commit -am 'Added some feature'`)

  4. Push to the branch (`git push origin my-new-feature`)

  5. Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.

  6. Create new Pull Request


This library aims to adhere to Semantic Versioning 2.0.0. Violations of this scheme should be reported as bugs. Specifically, if a minor or patch version is released that breaks backward compatibility, a new version should be immediately released that restores compatibility. Breaking changes to the public API will only be introduced with new major versions.

As a result of this policy, you can (and should) specify a dependency on this gem using the Pessimistic Version Constraint with two digits of precision.

For example:

spec.add_dependency 'cacheable_flash', '~> 4.0'


Licensed under the MIT License. See LICENSE for further details.