Intro

Embedding videos on a website is very easy, add a <video> tag to your source code and it just works. Most of the time.

The thing is: Both the operating system and Browser of your client must support the container and codecs of your video. To ensure playback on every device, you have to transcode your videos to one or more versions of which they are supported by every device out there.

In this card, I'll explore the available audio and video standards we have right now. The goal is to built a pipeline that...

CoffeeScript and JavaScript (ECMAScript) both have operators in and of. Each language use them for more than one purpose. There is not a single case where the same operator can be used for the same purpose in both languages.

Check if an object (or its prototype) has a property

CoffeeScript

var hasFoo = 'foo' of object

JavaScript

var hasFoo = 'foo' in object;

Iterate through all properties of an object
================================...

Code comments allow for adding human readable text right next to the code: notes for other developers, and for your future self.

As always, with great power comes great responsibility. Code comments can go wrong in many ways: they may become outdated, silently move away from the code they're referring to, restate the obvious, or just clutter files.

Good Comments

Here are some simple rules to keep your comments helpful:

Avoid stating what some code does – prefer the Why

Some say, perfect code would not need a single comment. Th...

Here are some popular mistakes when using nested forms:

• You are using fields_for instead of form.fields_for.
• You forgot to use accepts_nested_attributes in the containing model. Rails won't complain, but nothing will work. In particular, nested_form.object will be nil.
• The :reject_if option lambda in your accepts_nested_attributes call is defined incorrectly. Raise the attributes hash given to your :reject_if lambda to see if it looks like you expect.
• If you are nesting forms into nested forms, each model involved ne...

TL;DR Use the #remove_<mounted_attribute>! method to delete attachments. Also, save the record after removing the file!

As you know, Carrierwave file attachments work by mounting an Uploader class to an attribute of the model. Though the database field holds the file name as string, calling the attribute will always return the uploader, no matter if a file is attached or not. (Side note: use #present? on the uploader to check if the file exists.)

class User < ApplicationRecord
  mount :avatar, AvatarUploader
end

...

Say you have a User with a Carrierwave attribute #avatar:

class User < ActiveRecord::Base
  mount_uploader :avatar, AvatarUploader
end

When whitelisting the avatar field in the controller, you might do this:

  params[:user].permit(:avatar)

But you probably want this:

  params[:user].permit(:avatar, :avatar_cache, :remove_avatar)

In this example:

• :avatar_cache allows a newly upload image to persist through form roundtrips in the case of validation errors (something that isn't possible with Paper...

When requests arrive at the application servers simultaneously, weird things can happen. Sometimes, this can also happen if a user double-clicks on a button, for example.

This often leads to problems, as two object instances are modified in parallel maybe by different code and one of the requests writes the results to the database.

In case you want to make sure that only one of the requests "wins", i.e. one of the requests is fully executed and completed while the other one at least has to wait for the first request to be completed, you ha...

If you need to test some HTML, e.g. an embed code, you can use RubyMine's "scratch files":

1. File > New Scratch File (or Ctrl + Shift + Alt + Ins)
2. Select "HTML" as file type
3. Write or paste the HTML
4. Move your mouse to the upper right corner of the scratch file editor. Pick a browser to instantly open your file.

We can use ActiveRecord's where to add conditions to a relation. But sometimes our condition is not on the model itself, but on an associated model. This card explains multiple ways to express this condition using ActiveRecord's query interface (without writing SQL).

As an example we will use a User that has many Posts:

class User < ApplicationRecord
  has_many :posts
  scope :active, -> { tra...

TLS/SSL certificates are often used for HTTPS traffic. Occasionally a service may also use their TLS certificate to support public-key encrypting data (e.g. when it is part of the URI and visible to the user, but contains sensitive information).

Here is how to easily fetch such certificate data.

certificate = Net::HTTP.start('example.com', 443, use_ssl: true) { |http| http.peer_cert }
# => #<OpenSSL::X509::Certificate: subject=#<OpenSSL::X509::Name CN=www.example.org,...>

certificate.public_key
# => #<OpenSSL::PKey::RSA:0x...

To safely transport an arbitrary string within a URL, you need to percent-encode characters that have a particular meaning in URLs, like & or =.

If you are using Rails URL helpers like movies_path(:query => ARBITRARY_STRING_HERE), Rails will take care of the encoding for you. If you are building URLs manually, you need to follow this guide.

Ruby

In Ruby, use CGI.escape:

CGI.escape('foo=foo&bar=bar')
=> "foo%3Dfoo%26bar%3Dbar"

Do not ever use URI.encode or ...

Or: How to avoid and refactor spaghetti code

Please note that I tried to keep the examples small. The effects of the methods in this card are of course much more significant with real / more complex code.

What are the benefits of more modular code?

Code is written once but read often (by your future self and other developers who have to understand it in order to make changes for example). With more modular code you reduce the scope of what has to be understood in order to change something. Also, naming things gives you the opportunity t...

Imagine you want to write a cucumber test for a user-to-user chat. To do this, you need the test to work with several browser sessions, logged in as separate users, at the same time.

Luckily, Capybara makes this relatively easy:

Scenario:

Scenario: Alice and Bob can chat
  Given Alice, Bob, and a chat session
  When I am signed in as "Alice"
    And I go to the chat
    And I am signed in as "Bob" [session: bob]
    And I go to the chat [session: bob]
    And I send the message "Hello, this is Alice!"
  Then I should see "Hello, this ...