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...

Most browsers have built-in drag and drop support for different page elements like text and images. While this may be useful in most situations, it may become annoying in others. If you e.g. want to allow the user to scroll/move horizontally within a container by grabbing an item and moving the mouse, you will notice that nothing will move and you'll instead start dragging that element.

To disable this, add the following CSS to your content:

-webkit-user-drag: none
user-drag: none

-webkit-user-drag is only fully supported in ...

We had a card that described how to install multiple mysql versions using mysql-sandbox. Nowadays with the wide adoption of docker it might be easier to use a MySQL docker image for this purpose.

Create a new mysql instance

docker run --name projectname_db -e MYSQL_ROOT_PASSWORD=secret -p "33008:3306" -d --restart unless-stopped mysql:5.7

The port 33008 is a freely chosen free port on the host machine that will be used to establish a con...

You can scale background images in CSS to the container size using background-size (Demo).

Commonly, we use contain or cover because we want to preserve the image's aspect ratio.
If you do not want to do that, simply provide scaling values for X and Y:

background-size: 100% 100%

(a simple 100% would mean 100% auto and respect the image's aspect ratio)

SVGs with a viewBox will force their aspect ratio

The above may not work for you when ...

When using custom properties in your stylesheets, you may want to set a specific property value to an existing variable in your SASS environment. A pratical example would be a list of color variables that you've defined in colors.sass and that you would like to refer to in your stylesheets. However, simply assigning a variable will not work:

$my-great-blue: blue

:root
  --my-color: $my-great-blue

.sky
  background-color: var(--my-color)

The property value will not be valid and if you open the browser's inspection window, yo...

When giving a presentation where you do some coding, the font size you usually use is probably a bit too small and makes code hard to read for users on smaller screens or low-bandwidth connections when the image quality is lower.

Here are two solutions.

Presentation Mode

RubyMine offers a "Presentation Mode" which you can use. Simply navigate to View → Appearance → Enter Presentation Mode to enable it.
This will increase your code editor's font size as well as your UI and works nicely when sharing a single file.

However, some control...

When storing files for lots of records in the server's file system, Carrierwave's default store_dir approach may cause issues, because some directories will hold too many entries.

The default storage directory from the Carrierwave templates looks like so:

class ExampleUploader < CarrierWave::Uploader::Base
  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end
end

If you store files for 500k records, that store_dir's parent directory will have 500k sub-directories which will cause some...

When deleting a record in your Rails app, Carrierwave automatically takes care of removing all associated files.
However, the file's container directory will not be removed automatically. If you delete records regularly, this may be an annoyance.

Here is a solution which was adapted from the Carrierwave GitHub wiki and cleans up any empty parent directories it can find.

class ExampleUploader < CarrierWave...

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 ...

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 ...

When you have a hex color code, you can easily convert it into its RGB values using plain Ruby.

>> "#ff8000".match(/^#(..)(..)(..)$/).captures.map(&:hex)
=> [255, 128, 0]

You can use that to implement a simple "hex to CSS rgba value with given opacity" method:

def hex_color_to_rgba(hex, opacity)
  rgb = hex.match(/^#(..)(..)(..)$/).captures.map(&:hex)
  "rgba(#{rgb.join(", ")}, #{opacity})"
end

>> hex_color_to_rgba("#ff8000", 0.5)
=> "rgba(255, 128, 0, 0.5)"

If you need to support RGBA hex color codes,...

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...

We had the issue, that a VCR spec failed, after updating CarrierWave from version 0.11.0 to 1.3.2.
In this version, CarrierWave uses the gem SsrfFilter, which retrieves the IP addresses for the given hostname and replaces the hostname in the requested url with one of them.

It works with IPv4 addresses, but not with IPv6 addresses, because WebMock cannot handle those correctly:

uri = "#{protocol}://...

CarrierWave comes with a set of default configuration options which make sense in most cases. However, you should review these defaults and adjust for your project wherever necessary.

You will also find suggestions on what to change below.

Understanding the default configuration

Here is the current default config for version 2:

config.permissions = 0644
config.directory_permissions = 0755
config.storage_engines = {
  :f...

If your project depends on an old version of ImageMagick that you can no longer install in your system, you can choose the run an old ImageMagick in a Docker container.

Dockerized ImageMagick commands will only work with absolute path arguments. You need to boot a corresponding docker container once before using it.

Setting up Docker

If you haven't installed Docker yet, use our guide or the [official instructions](https://docs.docker.com/get-started/...

Recently I made an upgrade from Bootstrap 3 to Bootstrap 4 in a bigger project. Here are some tips how to plan and perform such an upgrade. The effort will scale with the size of the project and its structure. If your stylesheets already follow strict rules, it may take less time to adapt them to the new version.

Preparation

There are several gems and libraries that works well with bootstrap or provide at least stylesheets/plugins to easily integrate the bootstrap theme. But very often they only work with specific version or are no long...

I just finished migrating a project from the Asset Pipeline to Webpacker, this is what my diff to master looks like:

5.825 files changed, 44.805 insertions(+), 529.948 deletions(-)
warning: inexact rename detection was skipped due to too many files.
warning: you may want to set your diff.renameLimit variable to at least 5134 and retry the command.

There is no way me or my peer reviewer is able to parse 500k+ lines of code. Fortunately, git has ...

In long diffs, it can become impossible to spot small changes in larger blocks of moved code. This may be either a method that was moved from the top to the bottom of a file, or a long test file that was split in many.

Fortunately, Git offers a special highlighting mode that directs the reader's attention to relevant code parts:

git diff --color-moved=dimmed-zebra

It will dim lines that were moved around without changes, and highlight changed lines.
To easily use dimmed-zebra mode, configure an alias:

# ~/.gitconfig
[alias]
 ...

• Feature Queries (Edge 12+): Similar to @media queries, @supports blocks can be scoped to browsers that support a given declaration. There is CSS.supports() to do the equivalent in Javascript.

• backdrop-filter (Edge 17+, but not FF): Applying filters to what is visible through an element.

• [touch-action](https://d...

While both the alt attribute and the figcaption element provide a way to describe images, the way we write for them is different:

• alt descriptions should be functional
• figcaption descriptions should be editorial or illustrative

Generated Photos produces AI-generated face images.

This is useful for UI mockups where you don't want to show real people or copyrighted stock photography.

CSS variables are very different from preprocessor variables. While preprocessors use variables to compile a static piece of CSS, CSS custom properties are a reactive (i.e. live) part of the styles. Think of them like usual CSS properties that cascade, but have:

• A special syntax: CSS variables always start with a double-dash (--color)
• No inherent meaning: Defining a CSS variable will not change any styles in itself
• A special functionality: CSS variables can be used within the values of other properties, including CSS variables...

A flat folder structure can be cool if you have only a few folders but can be painful for huge amounts. We recently had this issue in a project with more than 100.000 attachments, where we used a structure like this /attachments/123456789/file.pdf.

Even the ls command lasted several minutes to show us the content of the attachments folder.

So we decided to use a more hierarchical structure with a limited maximum of folder per layer. Here are a few tips how to migrate your files to their new...