Some users might use Adblock Plus or similar browser plugins to reduce the number of ads displayed. If you run into an issue that your application or part of an application is blocked, this card will give you some guidance on how to debug it.

In general ad blocking is not an issue for most of our web apps. But if your application uses iframes or is embedded in another site it's more prone to it.

Blocked elements most of the time appear to the user as empty frames in the page. The indicator icon of the ad blocker also gives ...

A flaky test is a test that is often green, but sometimes red. It may only fail on some PCs, or only when the entire test suite is run.

There are many causes for flaky tests. This card focuses on a specific class of feature with heavy side effects, mostly on on the UI. Features like the following can amplify your flakiness issues by unexpectedly changing elements, causing excessive requests or other timing issues:

• Lazy loading images
• Autocomplete in search f...

If you want Sidekiq to be able to talk to Redis on staging and production servers, you need to add the following to your configuration:

# config/initializers/sidekiq.rb
require 'sidekiq'

Sidekiq.configure_client do |config|
  config.redis = { url: REDIS_URL }
end

Sidekiq.configure_server do |config|
  config.redis = { url: REDIS_URL }
end

The following step may be skipped for new Sidekiq 6+, since it isn't recommended anymore to use a global redis client.

# config/initializers/redis.rb
require 'redis'
require_relativ...

Within development and test environments, Rails is usually configured to show a detailed debug page instead of 404s. However, there might be some cases where you expect a 404 and want to test for it.

An example would be request-specs that check authorization rules. (If you use a gem like consul for managing authorization rules, you should always check these rules via power-specs. However, request-specs can be used as a light-weight version of integration tests here.)

In this case, Rails will replace the 404 page that you want to test ...

This RailsCast demonstrated a very convenient method to activate VCR for a spec by simply tagging it with :vcr.

For RSpec3 the code looks almost the same with a few minor changes. If you have the vcr and webmock gems installed, simply include:

# spec/support/vcr.rb
VCR.configure do |c|
  c.cassette_library_dir = Rails.root.join("spec", "vcr")
  c.hook_into :webmock
end

RSpec.configure do |c|
  c.around(:each, :vcr) do |example|
    name = example.metadata[:full_descripti...

Bookmarks for directories will be most helpful if you are forced to work in deeply nested projects. Then it's really helpful!

This makes use of the CDPATH variable. Similar to the PATH variable, which holds the list of directories which are searched for executables, CDPATH contains the list of directories that are available for cd. Besides the current directory (.), you can add others to that.

The trick is to add a directory for bookmarks to CDPATH.

First, create the directory with: mkdir ~/.bookmarks.

Then add the followin...

With cd .. you can navigate one directory up from the one you are at now. If you use that a lot, consider some handy aliases.

Add the following lines to your ~/.bashrc:

alias ..="cd .."
alias ...="cd ../.."
alias ....="cd ../../.."
alias .....="cd ../../../.."
alias ......="cd ../../../../.."

you can add even more aliases, but I usually loose track after too many levels and just jump to the directly directly, e.g. using its absolute path or its bookmark (see [this card](https://makandracards.com/makandra/504947-working-on-the-li...

Rails has the handy controller method send_file which lets us download files easily. We can decide whether the file should be downloaded (disposition: 'attachment') or shown in the browser (disposition: 'inline'). The default is disposition: 'attachment'.

Downloading files will not work when you are calling the controller action from an AJAX request. The browser will try to render the file and insert it in the DOM, which is never what you want.

Unpoly 2

Unpoly (sin...

It is generally discouraged to load your JavaScript by a <script src> tag in the <head>:

<head>
  <script src="app.js"></script>
</head>

The reason is that a <script src> tag will pause the DOM parser until the script has loaded and executed. This will delay the browser's first contentful paint.

A much better default is to load your scripts with a <script src defer> tag:

<head>
  <script src="app.js" defer></script>
</head>

A deferred script has many useful properties:

• I...

It seems like changing the HTTP_ACCEPT_LANGUAGE is not possible for a headless chrome.

• On Ubuntu the headless Chrome derives the Accept-Language from the operation system
• Adding the option options.add_argument('--lang=de') to the Capybara::Selenium::Driver has no effect
• Adding the preference options.add_preference('intl.accept_languages', 'de') to the Capybara::Selenium::Driver has only effects if the --headless option is skipped (see bug ticket #775911)
• Cha...

Formerly 301 (Moved Permanently) and 302 (Found) were used for redirecting. Browsers did implement them in different ways, so since HTTP 1.1 there are some new status codes which allow for finer distinctions.

The interesting part is how non-GET requests are handled by the redirect. It is preferrable to use the newer status code to avoid unexpected behavior.

303 See Other

The response to the request can be found under anot...

When using RestClient to make an HTTP request, it will raise an exception when receiving a non-successful response.
HTTP status codes like 422 or 403 might be totally expected when talking to APIs, so plastering your code with rescue RestClient::Exception or similar can feel annoying.

It may not be intuitive, but the readme says you can also pass a block to methods like RestClient.get or RestClient::Request.execute. In that case, RestClient will not raise ...

The Node Version Manager allows installing multiple NodeJS versions and switching between them.
By default, it does not automatically switch versions when entering a directory that holds a .nvmrc file.

The project's readme document offers a bash function which calls nvm use after each cd. In fact, it replaces cd in your bash.

I did not want to do that, but instead use the $PROMPT_COMMAND feature. So here is my take on it.
Note that it is much shorter, it probably does a f...

When dealing with external data sources, you may have to deal with improperly encoded strings.
While you should prefer deciding on a single encoding with the data-providing party, you can not always force that on external sources.
It gets worse when you receive data with encoding declaration that does not reliably fit the accompanying string bytes.

Here is a Ruby class that helps converting such strings to a proper encoding.
Note that it tries several approaches of changing the encoding. **This is not a silver bullet and may or may not work...

When a Ruby version gem has a letter in its version number, it is considered a pre-release:

• 1.0.0.rc1
• 2.3.0.alpha2
• 3.0.0.beta3
• 4.0.0.pre.rc2

Even if a pre-release gem has the highest version number, it is never installed unless the user explictily requested the version:

gem install foobar --version="=2.3.0.alpha2"

Also bundle update will never update a stable version to a pre-release version unless the user explicitly requests it in the Gemfile:

gem 'foobar', '=2.3.0.alpha2'

A note on Semanti...

Webpack builds can take a long time, so we only want to compile when needed.

This card shows what will cause Webpacker (the Rails/Webpack integration) to compile your assets.

When you run a dev server

While development it is recommended to boot a webpack dev server using bin/webpack-dev-server.

The dev server compiles once when booted. When you access your page on localhost before the initial compilation, the page may load without assets.

The ...

Use rules to include or exclude jobs in pipelines.

Rules are evaluated in order until the first match. When a match is found, the job is either included or excluded from the pipeline, depending on the configuration. The job can also have certain attributes added to it.

rules replaces only/except and they can’t be used together in the same job. If you configure one job to use both keywords, the linter returns a key may not be used with rules error.

GitLab 12.3 introduced rules. You can use them in your .gitlab-ci.yml in your proj...

Installing gems on a server that has no access to the internet (especially rubygems.org) requires to bundle the gems into the repository itself. This requires to adjust the bundle config in the repository.

1. Execute the following commands to configure bundler:

bundle config set --local path vendor
bundle config set --local disable_shared_gems true

Note

For Bundler < 2 you have to omit the "set": bundle config --local name value.
See here: [https://bundler.io/v1.17/man/bundle-config.1.html](https://bundler.io/v1.17/man...

Preparation

To attach files to your records, you will need a new database column representing the filename of the file. To do this, add a new migration (rails g migration <name>) with the following content:

class AddAttachmentToNotes < ActiveRecord::Migration[6.0]
  def change
    add_column :notes, :attachment, :string
  end
end

Don't forget to rename the class and change the column details to fit your purpose. Run it.

1) Deliver attachments through Rails

The first way is to store your Carrierwave attachments not ...

We prefer to run our end-to-end tests with headless Chrome. While it's a very stable solution overall, we sometimes see the headless Chrome process freeze (or the Capybara driver losing connection, we're not sure).

The effect is that your test suite suddenly stops progressing without an error. You will eventually see an error after a long timeout but until then it will seem that your suite is frozen. If you're also using [capybara-screenshot](https:/...

When your Rails application server raises error, Capybara will fail your test when it clears the session after the last step. The effect is a test that passes all steps, but fails anyway.

Capybara's behavior will help you to detect and fix errors in your application code. However, sometimes your application will explode with an error outside your control. Two examples:

• A JavaScript library references a source map in its build, but forgets to package the source map
• CarrierWave cleans up an upload or cache file after the record was delet...

The ActionDispatch module of Rails gives you the helper method flash to access the flash messages in a response.

describe PostsController, type: :request do

  describe 'update' do

    it 'shows a success message on update' do
      post_record = create(:post)

      put "/posts/#{post_record.id}"

      # Same as @request.flash[:alert]
      expect(flash[:alert]).to eq('Post updated successfully.')
    end

  end


end