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Canceling promises

The cancelable promises proposal was withdrawn some time ago.

The new standard way is that your long-running function take a AbortSignal { signal } property. The caller can use this signal to send an abort request to your function. Upon receiving the request, your function should reject its promise with an error.

Async browser functions like fetch() reject their promises with a `new DOMException('Message here', 'Abo...

Transporting blank values in URL queries

URLs can transport key/value pairs ("parameters") using this syntax:


If the value is blank, mind these subtle differences:

URL Meaning
/path?foo= Parameters have a key foo. Its value is an empty string.
/path?foo Parameters have a key foo. Its value is null.
/path Parameters have no key foo.

Git diff: Deemphasizing code that was only moved around

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. See this SO answer for an illustra...


Restarting all God tasks

To restart all tasks monitored by God, don't use god restart. This command is only meant to soft-restart a given process or group.

Instead you should:

god stop
god terminate
god start -c yourgodconfig.god

Best practices: Large data migrations from legacy systems

Migrating data from a legacy into a new system can be a surprisingly large undertaking. We have done this a few times. While there are significant differences from project to project, we do have a list of general suggestions.

Before you start, talk to someone who has done it before, and read the following hints:

Understand the old system

Before any technical considerations, you need to understand the old system as best as possible. If feasible, do not only look at its API, or database, or frontend, but let a user of the old system sho...

Linked contentRepeats

Devise: Don't forget to lock users with soft delete

There are two ways to lock a user in devise.

  1. Using the lockable module
  2. Customizing the user account status validation when logging in.

It depends on your requirements which methods works best.

Locking a user on soft delete

We recommend to use option 2 when you want to couple the lock to the m...

How to build a fully custom TinyMCE 5 dialog

TinyMCE is a WYSIWYG editor which is quite customizable.

  1. Add a custom button to the tinyMCE toolbar and tell tinyMCE to open a dialog with the route to your dialog's view.
  // ...
  toolbar: 'myCustomButton',
  setup: function(editor) {
      editor.ui.registry.addButton('myCustom Button', {

How to test inside iframes with cucumber / capybara

When testing with Cucumber / Caypbara, iframes are ignored, so you can't interact with them.

To interact with your iframe, you have to explicitly tell your driver to use it.
You can reference your iframe either through it's id, or if none given, by it's number:

When /^(.*?) inside the (.*?). iframe$/ do |nested_step, frame_number|
  page.within_frame(frame_number.to_i) do
    step nested_step

When /^(.*?) inside the (.*?). iframe:$/ do |nested...

Ruby < 2.4: Downcasing or upcasing umlauts

Using .downcase or .upcase on strings containing umlauts does not work as expected in Ruby versions before 2.4. It leaves the umlauts unchanged:

=> "Über"

=> "Ärger"

The very same applies for french accents (Thanks Guillaume!):

"Être ou ne pas être, telle est la question".downcase
=> "Être ou ne pas être, telle est la question"

Obviously, this leads to problems when comparing strings:

"Über".downcase == "über"
=> false

In Rails you can use ActiveSupports' [multib...

Linked contentRepeats

Ruby's percent notation can do more than strings

Percent Notation

We already know that that we can create strings using the percent notation:

%{<foo="bar's ton">} is perfectly fine Ruby.


But there is more. The curly brackets ({}) are interchangable with most unicode characters (e.g. square brackets[]).
Furthermore, you can add a "modifier" to the percent notation to control the return type of th...


Testing shared traits or modules without repeating yourself

When two classes implement the same behavior (methods, callbacks, etc.), you should extract that behavior into a trait or module. This card describes how to test that extracted behavior without repeating yourself.

Note that the examples below use Modularity traits to extract shared behavior. This is simply because we like to do it that way at makandra. The same techniques apply for modules and overriding self.included.


Ruby: How to keep split delimiter (separate, or as part of substrings)

Ruby's String#split returns an array of substrings from the given string. Usually, this is missing the split characters:

>> 'user@example.com'.split('@')
=> ["user", "example.com"]

If you want to join those parts later on, you might know the split character and can just use it to join explicitly.
But if you split by a regular expression (for a set of split characters) that information is lost:

>> 'user@example.com'.split(/[@\.]/)
=> ["user", "example", "com"]

You can use a capture group to make those characters ...


Running Capybara tests in headless Chrome

Headless Chrome is a way to run the Chrome browser without a visible window.

Configuring Capybara

Configure the Capybara driver like this:

Capybara.register_driver :selenium do |app|
  options = Selenium::WebDriver::Chrome::Options.new
  options.add_argument('--headless') unless ENV.key?('NO_HEADLESS')
  options.add_option('w3c', false)
  options.add_emulation(device_metrics: { width: 1280, height: 96...

SSHKit 1.9.0 failure for Capistrano deploy

SSHKit 1.9.0 might fail with the following error, when trying to deploy a Rail application. Upgrading the gem to version 1.21.0 fixed the issue.

Traceback (most recent call last):
	17: from /home/user/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/sshkit-1.9.0/lib/sshkit/runners/parallel.rb:12:in `block (2 levels) in execute'
	16: from /home/user/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/sshkit-1.9.0/lib/sshkit/backends/abstract.rb:29:in `run'
	15: from /home/user/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/sshkit-1.9....

Whenever requires you to set the application attribute in the Capistrano config

Whenever requires you to set the application attribute in your Capistrano configuration. Otherwise your cronjobs are created multiple times.

Example entry in config/deploy.rb:

set :application, 'some-app' # allows "set :whenever_identifier, ->{ "#{fetch(:application)}_#{fetch(:stage)}" }" to work as expected


Then the crontab will look like this:

# Begin Whenever generated tasks for: some-app_staging

34 2...
Linked content


This is an informational site about video and how it works. We started by talking about Playback, next we added content about Delivery. Stay tuned for more about Processing and Capture.


Case sensitivity in PostgreSQL

PostgreSQL, unlike MySQL, treats strings as case sensitive in all circumstances.

This includes

  • comparison with = and LIKE
  • collision detection in unique indexes

Usually this is fine, but some strings (like emails and usernames) should typically be treated as case insensitive.

There are a few workarounds available:

  • use the citext extension (not recommended)
  • use ILIKE instead of LIKE
  • use Postgres' lower() function
  • add an index on lower(email)

Probably th...


Take care of indentation and blank lines when using .erb for plain text emails

Building plain text emails with an .erb template doesn't allow you to indent code like you normally do in HTML mails.


<%= 'foo' if bar %>

"\n" if bar is false

"foo\n" if bar is true

<%= nil %>


<% if true %>
  <%= 'foo' %>
<% end %>  

" foo"

<%= 'foo' %>

<%= 'bar' %>



Write unindented code to get the expected result.

<% if bar %>
<%= 'bar' %>
<% end %>
<%= 'foo' %>
<%= 'bar' %> 
  • Use [Form Models](https://github.com/makandra...
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