When you need to add a event listener to hundreds of elements, this might slow down the browser.

An alternative is to register an event listener at the root of the DOM tree (document). Then wait for events to bubble up and check whether the triggering element (event.target) matches the selector before you run your callback.

This technique is called event delegation.

Performance considerations

Because you only register a single listener, registering is ...

When your Cucumber feature needs to browse the page HTML, and you are not sure how to express your query as a clever CSS or XPath expression, there is another way: You can use all and find to grep through the DOM and then perform your search in plain Ruby.

Here is an example for this technique:

Then /^I should see an image with the file...

If you already selected an element and want to get its parent, you can call find(:xpath, '..') on it.

To get the grand-parent element, call find(:xpath, '../..').

Example

Find a link which contains a twitter icon and check that it links to the correct page:

<a href="http://twitter.com/">
  <i class="icon is-twitter"></i>
</a>

link = page.find("a .icon.is-twitter").find(:xpath, '..')
expect(link[:href]).to eq("http://twitter.com/")

About XPath

There is a good overview on XPath syntax on [w3schools](htt...

For Selenium tests, your browser starts in your local timezone, or whatever your system's environment specifies.
This is usually good enough. To test any timezone-dependent behavior in Chrome, you can change the time zone using the Chrome DevTools Protocol.

Example

Chrome accepts any IANA time zone name, like "Europe/Berlin" or "Asia/Tokyo".
Here is the relevant command for Capybara:

page.driver.browser.execute_cdp('Emulation.setTimezoneOverride', timezoneId: 'Asia/Tokyo')
``...

Why Rails has multiple schema formats

When you run migrations, Rails will write your current database schema into db/schema.rb. This file allows to reset the database schema without running migrations, by running rails db:schema:load.

The schema.rb DSL can serialize most common schema properties like tables, columns or indexes. It cannot serialize more advanced database features, like views, procedures, triggers or custom ditionaries. In these cases you must switch to a SQL based schema format:

# in application.rb
config.a...

DirectUpload allows you to upload files to your file storage without having to wait for the form to submit. It creates AJAX requests to persist the file within your form and wraps them in a little API. This card will show you how to use it in order to create in-place file uploads with progress and a remove button.

This is basic functionality, you may add additional elements, styles and logic to make this look fancy, but the core functionality is the same. I created a file upload that looks like this:

![Image](/makandra/625023/attachments/3...

Here is a workaround for when you want to use text-wrap: balance but must also render nicely for browsers that don't support it (mostly Safari <17.5).

Step 1: Put some <br>s into your HTML

First, place explicit line breaks that should work for most cases.
This depends on your use case and is affected by e.g. container widths or user content.

<div class="my-element">
  <p>
    Average score
    <br>
 ...

ActiveStorage does not provide any built-in way of implementing authentication for the available DirectUpload endpoint in Rails. When using DirectUpload as JS wrapper in the frontend, be aware that its Rails endpoint is public by default, effectively allowing anyone to upload an unlimited amount of files to your storage.

The DirectUploadController from @rails/activestorage bypasses your form controller because it uploads the file using an AJAX request that runs directly, before any form roundtrip happens. This is a comfortable solutio...

Sometimes you want to fetch associations for an ActiveRecord that you already loaded, e.g. when it has deeply nested associations.

Edge Rider gives your models a static method preload_associations. The method can be used to preload associations for loaded objects like this:

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
    @user.preload_associations(threads: { posts: :author }, messages: :sender)
  end
end

The attached initializers re...

Form fields can be rendered as noneditable by setting the disabled or the readonly attribute. Be aware of the differences:

disabled fields

• don’t post to the server
• don’t get focus
• are skipped while tab navigation
• available for button, fieldset, input, select, textarea, command, keygen, optgroup, option

Browser specific behavior:

• IE 11: text inputs that are descendants of a disabled fieldset appear disabled but the user can still interact with them
• Firefox: selecting text in a disabled text field is no...

For long running scripts it is useful to show a indicator for the progress in the terminal. Alternatively you can use a gem like paul/progress_bar.

count = User.count
index = 0

User.find_each do |user|
  printf("Progress: %.2f%%\r", index.to_f / count * 100)
  user.update!(role: 'member')
  index += 1
end

Preview video

SVG files often contain redundant information, like editor metadata or hidden elements. When esbuild handles your static assets, you can easily optimize SVG files using svgo as a plugin. Here is how to do it.

Adding svgo as an esbuild plugin

1. Add the svgo package to your project's package.json
2. Adjust your esbuild.config.js like so:

const esbuild = require('esbuild')
const svgo = require('svgo')

const options = {
  // ...
  loader: {
    // ...
    '.svg': 'copy', // this may be different...

PostgreSQL can cosplay as a full-text search engine. It doesn't have the features or fidelity of ElasticSearch or Algolia, but it's good enough if you just need to search and rank large volumes of text.

This card will teach you how to index, search and rank your Rails models in a PostgreSQL full-text index. We will do this without using any gems aside from ActiveRecord. While there are gems like pg_search or pg_fulltext, manual integration requires very...

Method delegation in Rails can help you to keep your code organized and avoid deep call chains (law of demeter) by forwarding calls from one object to another. Rails provides several ways to accomplish this. Below is a concise overview of the most common approaches:

Single-Method delegation with delegate

Use the built-in delegate method from ActiveSupport to forward specific methods:

class User < ApplicationRecord
  has_one :profile

  delegate :full_name, :age, to: :profile, prefix: true
end

• `delegate: full_name, :age...

There are several ways to run a single spec. I usually copy the spec file path with the line number of the example and pass it to the RSpec binary: bin/rspec spec/models/user_spec.rb:30 (multiple line numbers work as well: :30:36:68). Another is to tag the example with focus: true or to run the example by matching its name.

In this card I'd like to ...

All columns of a model's database table are automagically available through accessors on the Active Record object.

When you need to specialize this behavior, you may override the default accessors (using the same name as the attribute) and simply call the original implementation with a modified value. Example:

class Poet < ApplicationRecord

  def name=(value)
    super(value.strip)
  end

end

Note that you can also avoid the original setter and directly read/write from/to the instance's attribute storage. However this is dis...

When HTTP clients make an request they can define which response formats they can process. They do it by adding a header to the HTTP request like this:

Accept: application/json

This means the client will only understand JSON responses.

When a Rails action is done, it will try to render a template for a format that the client understand. This means when all you are HTML templates, a request that only accepts application/json will raise an error:

An ActionView::MissingTemplate occurred in pages#foo:
  Missing templa...

Within a Flexbox layout, there are multiple CSS attributes that may affect a child's basis (the initial width before flexing). You might be confused how flex-basis, width, min-width and the intrinsic width of your content play together.

The attached article explains the differences. In summary:

• If a flex-basis is set, that is used as the basis
• If no flex-basis is set, the width is used as the basis
• If neither flex-basis nor width is set, the content...

Most forms have a single submit button that will save the record when pressed.

Sometimes a form needs additional submit buttons like "accept" or "reject". Such buttons usually attempt a state transition while updating the record.

To process a form with multiple buttons, your server-side code will need to know which button was pressed. To do so you can give each submit button a different [formaction] attribute. This will override the ...

You can use constraints in your routes.rb to avoid getting ActionView::MissingTemplate errors when wrong routes are called. Instead, the user will see a 404.

If you want multiple routes to use the same constraint you can use the block syntax:

constraints(format: 'html') do
  resources :pages
  resources :images
end

If you want constraints only on certain routes, you can do:

get '/users/account' => 'users#account', constraints: { format: 'html' }

Tip

You can also avoid this error type through [format con...

Haml renders HTML with indentation reflecting the nesting level of elements. When it comes to white-space preserving content, this may become a problem: the content will be rendered including the HTML indentation.

Problematic: Preserved Indentation

.nest
  %span Reference
  %pre
    = content

<div class="nest">
    <span>Reference</span>
    <pre>
        Hello
        World
    </pre>
</div>

Better: Without Extra Indentation

Render with tilde ~ instead of equal...

This card is a general reminder to avoid the short version of a command option in shared code. It's much easier to understand a command and search for an option when it's written out.

You can still use the short version of the options in your own terminal or in code snippets that are more useful when they are very compact. For the latter case you often see a description of the command options one line below e.g. in posts on stackoverflow.

Example good (in code):

/usr/bin/gpg --output password.txt --decrypt password.txt.gpg

...

tl;dr

git checkout is the swiss army of git commands. If you prefer a semantically more meaningful command for restoring tasks, use git restore instead.

With this command you can ...

• ... do unstaging - git restore --staged
• ... discard staged changes - git restore --staged --worktree
• ... discard unstaged changes - git restore
• ... restore deleted files - git restore
• ... restore historic versions - git restore --source
• ... recreate merge conflicts - git restore --merge
• ... specifiy...