HOWTOs for Ruby on Rails and JavaScript

Capo: putting <head> content into the right order

How you order elements in the <head> can have an effect on the (perceived) performance of the page.
This script helps you identify which elements are out of order.

Also available as a Chrome Extension. It shows the actual order of head elements, and suggests an optimal order for page performance.

github.com

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Linux: How to make a terminal window title reflect the current path

By default, your terminal emulator (Gnome Terminal, Terminator, etc.) sets some kind of window title to reflect the shell type you are running (e.g. /bin/bash).
This is most often not too helpful, but you can change that from your shell.

To set a specific title, print an escape sequence like this:

echo -en "\033]0;Hello\a"

You can easily include the current path:

echo -en "\033]0;$(pwd)\a"

Or, to replace your home directory's part with a tilde:

echo -en "\033]0;$(pwd | sed -e "s;^$HOME;~;")\a"

Or,...

terminal-title.gif

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About Ruby's conversion method pairs

Ruby has a set of methods to convert an object to another representation. Most of them come in explicit and implicit flavor.

explicit	implicit
`to_a`	`to_ary`
`to_h`	`to_hash`
`to_s`	`to_str`
`to_i`	`to_int`

There may be even more.

Don't name your methods like the implicit version (most prominently to_hash) but the like the explicit one.

Explicit conversion

Explicit conversion happens when requesting it, e.g. with the splat opera...

stackoverflow.com

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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.
To easily use dimmed-zebra mode, configure an alias:

# ~/.gitconfig
[alias]
 ...

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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.

Example
---...

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How to: Run bundle install in parallel

You can run bundle install in parallel. This might be helpful for development, where you often install many new gems when switching between projects.

Find out the number of processors you have:

lscpu

Set the config in your ~/.bundle/config globally (replace 8 with your number of proccessors):

bundle config jobs 8

Note

If you suspect parallel execution for bundling issues, you can try serially with bundle install --jobs 1.

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netstat: How to show listening ports

Sometimes it's necessary for you to check which ports are in use on your local machine and which process is using it. To list this information you can use the following command (which is pretty easy to memorize for Germans 🌷):

sudo netstat -tulpn

t: tcp
u: udp
l: listening ports
p: process
n: network

Use sudo to see the name of the process.

Finding open ports in the netstat output

You should look for rows with State: LISTEN.

Rows for local address 127.0.0.1 or...

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Raising JavaScript errors in Ruby E2E tests (RSpec, Cucumber)

A JavaScript error in an E2E test with Selenium will not cause your test to fail. This may cause you to miss errors in your frontend code.

Using the BrowserConsole helper below you can check your browser's error console from your E2E tests.

The following will raise BrowserConsole::ErrorsPresent if there is an error on the browser console:

BrowserConsole.assert_no_errors!

Ignoring errors

You can ignore errors by their exact message:

BrowserConsole.ignore('Browser is burning')

You can ignore errors with me...

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Don't assert exceptions in feature specs

As we are slowly switching from Cucumber scenarios to RSpec feature specs, you might be tempted to write assertions like this one:

feature 'authorization for cards management' do
  let(:guest_user) { create(:user, :guest) }

  scenario "rejects guest users from adding new cards", js: true do
    sign_in guest_user

    expect { visit new_cards_path }.to raise_error(Consul::Powerless)
  end
end

While this might work under certain circumstances¹, there is a good chance you'll see two exceptions when running this single spec:

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How to pretty print all values in a Redis database

With this Ruby script you can print all values in a Redis database to your console (derived from this bash script).

Note: Do not run this command in production. This is for debugging purposes only.

def pretty_print_redis(redis)
  redis.keys.each_with_object({}) do |key, hash|
    type = redis.type(key)

    hash[key] = case type
    when 'string'
      redis.get(key)
    when 'hash'
      redis.hgetall(key)
    when 'list'
      redis.lrange(key, 0, -1)
    when 'set'
      redis.smembers(...

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Better HTML forms: use type, inputmode, enterkeyhint and autocomplete

Web forms can be made much more usable with a few HTML attributes. Short summary:

type: Tells browsers about the input data type. Mobile browsers will select a virtual keyboard based on this value. Some browsers will add simple validation, e.g. for type email.
inputmode: Direct hint about the virtual keyboard to use. Inferred from type, but can be very handy when ...

adactio.com

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Byebug cheatsheet

Context and further resources

Even though you can get 90% of debugging done with up to 5 basic byebug commands, it comes in handy with it's features for many use cases beyond that to make your life easier.

For this cheatsheat I tried to structure the most useful commands by different use cases, such that a practical oriented overview of all the commands can be gathered by going over this cheatsheet. For some commands I added some tips for their usage and further details on their subcommands

For most of the commands shortl...

gist.github.com

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Bundler in deploy mode shares gems between patch-level Ruby versions

A recent patch level Ruby update caused troubles to some of us as applications started to complain about incompatible gem versions. I'll try to explain how the faulty state most likely is achieved and how to fix it.

Theory

When you deploy a new Ruby version with capistrano-opscomplete, it will take care of a few things:

The new Ruby version is installed
The Bundler version stated in the Gemfil...

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Ruby: Referencing global variables with the built-in English library

tl;dr

Don't forget require 'English' if you use a named global such as $LAST_MATCH_INFO. Otherwise this could result in an annoying bug.

With Ruby's build-in library English you can reference global variables with an english name. This makes you code easier to read and is also suggested by Rubocop's Style/GlobalVars cop.

Example before:

if 'foo' =~ /foo/
  puts $~[1] # => foo
end

Example af...

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How to write modular code

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...

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How to open files from better_errors with RubyMine on Linux

I recently noticed that better_errors allows you to to open files from within your favorite editor. However it was not so easy to get rubymine:// links to work on Gnome/Linux. Here is how it finally worked for me:

Step 1: Add a Desktop launcher

Add this file to ~/.local/share/applications/rubymine.desktop:

[Desktop Entry]
Version=1.0
T...

better_errors_file_opener.gif

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Chromedriver: Connect local chromedriver with docker

Debugging your integration tests, that run a headless Chrome inside a docker image, is tricky.

In many cases you can connect your Chrome to a remote docker container like docker-selenium, which should be the preferred way when you try to inspect a page within your integration test.

Otherwise you might be able to start your docker container with --net=host and access your local chromedriver in the host address space host.docker.internal.

If both options above don't work for you here is a...

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What is a reduction and why Fibers are the answer for Ruby concurrency | julik live

The linked article provides a good overview of the various concurrency primitives in Ruby, and what's changing in Ruby 3.

live.julik.nl

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Guide to localizing a Rails application

Localizing a non-trivial application can be a huge undertaking. This card will give you an overview over the many components that are affected.

When you are asked to give an estimate for the effort involved, go through the list below and check which points are covered by your requirements. Work with a developer who has done a full-app localization before and assign an hour estimate to each of these points.

Static text

Static strings and template text in app must be translated: Screens, mailer templates, PDF templates, helpe...

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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...

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How to Make Your Code Reviewer Fall in Love with You

Why improve your code reviews?
Improving code review technique helps your reviewer, your team, and, most importantly: you.
Learn faster: If you prepare your changelist properly, it directs your reviewer’s attention to areas that support your growth rather than boring style violations. When you demonstrate an appreciation for constructive criticism, your reviewer provides better feedback .
Make others better: Your code review techniques set an example for your colleagues. Effective author practices rub off on your teammates, which...

mtlynch.io

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PostgreSQL: How to use with_advisory_lock to prevent race conditions

If you want to prevent that two processes run some code at the same time you can use the gem with_advisory_lock.

What happens

The thread will wait indefinitely until the lock is acquired.

While inside the block, you will exclusively own the advisory lock.

The lock will be released after your block ends, even if an exception is raised in the block.

This is usually required if there is no suitable database row to lock on.

Example

You want to generate a...

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Allow capybara to click on labels instead of inputs for checkboxes

Within Capybara you most certainly use the #check- and #uncheck-method to (un)check checkboxes.
But there's one problem, if you want to test a custom styled checkbox, which hides its <input>-Tag:

The methods cannot (un)check checkboxes without an visible <input>.
The error message will be something like: Unable to find visible checkbox "Some label" that is not disabled

Solution 1

Use the keyword argument allow_label_click: true within the method call.
So instead of check('Some label'), use `check('Some label', allow...

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Fast rubocop autocorrection alias

The rubocop binary has a few interesting flags:

rubocop (using the --parallel default ) scans the current repository for linting issues while using multiple CPU cores
rubocop -a (or --autocorrect) safely corrects most offenses while doing a sequential scan
rubocop -A (or --autocorrect-all) also tries to correct unsafe suggestions

Autocorrection takes significantly longer on large projects because of the sequential nature.
To speed things up, you can use the following alias. It first checks in parallel if any files...

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