It can be hard to understand what causes a browser scroll smoothly or instantly. CSS, JavaScript and the browser settings all have options to influence the scroll behavior. They all interact with each other and sometimes use the same words for different behavior.

CSS

Scrolling elements can use the scroll-behavior CSS property to express a preference between smooth and instant scrolling.

Preferring instant scrolling

CSS can prefer instant scrolling behavior:

html {
  scroll-behavior: auto; /* the default */
}

An `aut...

Say you wrap your index view in a form to apply different filters like pagination or a search query. On submit, your index view changes when the filters are applied (through up-submit and up-target). Now you want to enable more data-specific filters using a separate "Filters" button that opens a popup to not overload your UI.

Filter bar:

Filter popup:

The problem is tha...

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')
``...

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...

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...

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...

Hint

If you are using our opscomplete.com hosting we can set all environment variables mentioned below for your deployment on request.

If you're lucky DO_NOT_TRACK=1 opts you out of CLI telemetry - it's not widely adopted. When you're using any of the libraries below, I'd rather opt out explicitly:

Yarn

https://yarnpkg.com/advanced/telemetry (Since: Version 2.2)

Disable for a project:

#...

Elements can be hidden and shown by toggling the display property. However, this is not animatable, so we often turn to opacity. At opacity: 0, the element is hidden, and with a nice transition on that property, it can be faded in and out smoothly.

Yet, opacity only hides visually, not technically: the element is still focusable and visible to screen readers. So, how can we fade an element while maintaining accessibility?

Enter visibility. It also hides elements, bu...

Starting with ChromeDriver 127, if your application displays a beforeunload confirmation dialog, ChromeDriver will immediately close it. In consequence, any automated tests which try to interact with unload prompts will fail.

This is because ChromeDriver now follows the W3C WebDriver spec which states that any unload prompts should be closed automatically.
However, this applies only to "HTTP" test sessions, i.e. what you're using by default. The spec also defines that bi-directional test se...

esbuild comes with a minifier that is good enough for most cases. If you're looking to squeeze out as many bytes as possible, you can consider compressing with Terser instead.

Using Terser will increase your build times significantly, but produce the smallest output:

| | Terser (3 pass) | Terser (1 pass) | esbuild |
|----------------------------|-----------------------|------------------|-------...

Terser is a really good minifier ("compressor") for JavaScript code. I'm often surprised by the thoughtfulness of its compressed output.

Let's take this function:

function fn() {
  if (a) {
    return 'foo'
  } else if (b) {
    return 'foo'
  } else {
    return c()
  }
}

console.log(fn())

Terser will reduce this to the following code:

console.log(a||b?"foo":c())

Note how:

• The if statement has been replaced by a tertiary expression. This is often less readable, but it doesn't matter in c...

testing-library are widely used testing utilities libraries for javascript dependent frontend testing. The main utilities provided are query methods, user interactions, dom expectations and interacting with components of several frontend frameworks, which allows us to worry less about the details happening in the browser and focus more on user centric tests instead!

Some of the time you will find a necessity to use methods like [waitFor](https://testing-library.com/docs/dom-testing-library/api-async/...

Reacting on a class getting added can be done with a mutation observer. Example:

const items = document.querySelectorAll('.item')
const expectedClass = 'active'
const activeObserver = new MutationObserver((mutations) => {
  mutations.forEach((mutation) => {
    if (mutation.target.classList.contains(expectedClass) {
      // Do something
    }
  })
})
items.forEach(item => activeObserver.observe(item, { attributes: true, attributeFilter: ['class'] }))

Note that this is not a generic solution – it makes a few assumptions to simplif...

I recently stumbled over a quirk in the way Ruby handles local variables that I find somewhat dangerous.

Consider:

def salutation(first_name, last_name = nil)
  if last_name
    full_name = "#{first_name} #{last_name}"
  end 
  "Hi #{full_name}"
end 

This is obviously wrong, full_name is unset when last_name is nil.

However, Ruby will not raise an exception. Instead, full_name will simply be nil, and salutation('Bob') returns 'Hi '.

The same would happen in an else branch:

def salutation(fi...

Modern JavaScript includes Intl.NumberFormat to format numbers in different formats and locales.
In this card, we describe a wrapper for it that humanizes a given number of seconds in the "next best" unit, like seconds, minutes, etc.

Example usage

>> new Duration(42).humanized()
=> '42 Sekunden'
>> new Duration(123456).humanized()
=> '1 Tag'
>> new Duration(123456).humanized('es')
=> '1 día'

Code

Here is the code ...

This card shows an uncommon way to retrieve a file using selenium where JavaScript is used to return a binary data array to Ruby code.

The following code example retrieves a PDF but the approach also works for other file types.

require "selenium-webdriver"

selenium_driver = Selenium::WebDriver.for :chrome
selenium_driver.navigate.to('https://example.com')
link_to_pdf = 'https://blobs.example.com/random-pdf'

binary_data_array = selenium_driver.execute_script(<<-JS, link_to_pdf)
  const response = await fetch(arguments[0])

  if (!r...

Debouncing a method call delays its execution until after a specified time has passed.
If it's called again before that time has passed, its execution is delayed again.

This technique is commonly used to improve performance when code would be run more often than it needs to.
One example for that are scroll event handlers in JavaScript: You want to react to a user scrolling, but it's enough to do that when they have stopped scrolling.

Here is a small JavaScript function that you can use for that:

function debounce(callback...

As we're switching from PT to Linear, I've updated the existing bash script to work for commits that are referencing Linear IDs.

A core benefit of our convention to prefix commits by their corresponding issue ID is that we can easily detect commits that belong to the same issue. You can either do that manually or use the bash script below. It can either be placed in your .bashrc or a...

Your commit messages should include the ID of the issue your code belongs to.
Our preferred syntax prefixes the issue title with its ID in brackets, e.g. [FOO-123] Avatars for users.
Here is how to generate that from an issue in Linear.

Add a new link to your browser's bookmarks bar with the following URL.

javascript:(() => {
  if (document.querySelector('[data-view-id="issue-view"]')) {
    const [id, ...words] = document.title.split(' ') ;
    prompt('Commit message:', `[${id}] ${words.join(' ')}`)
  } else {
    alert('Open issue...

This card describes four variants, that add a more intuitive workflow when working with nested attributes in Rails + Unpoly:

1. Without JS
2. With HTML template and JS
3. With HTML template and JS using dynamic Unpoly templates
4. Adding Records via XHR and JS

Example

For the following examples we use a simple data model where a user has zero or more tasks.

tl;dr When browsers start to adapt proposals from Open UI, it might not be necessary to use any 3rd party libraries to have nice components and controls in web applications e.g. selects. It would require only a minimum of CSS and Javascript to get them working and looking good.

The purpose of the Open UI, a W3C Community Group, is to allow web developers to style and extend built-in web UI components and controls, such as <select> dropdowns, checkboxes, radio buttons, and date/color pickers.

To do that, we’ll need to fully speci...

You can chain multiple Capybara matchers on the page or any element:

expect(page)
  .to have_content('Example Course')
  .and have_css('.course.active')
  .and have_button('Start')

When you chain multiple matchers using and, [Capybara will retry the entire chain](https://github.com/teamcapybara/capybara/blob/c0cbf4024c1abd48b0c22c2930e7b05af58ab284/lib/capybara/rspec/matc...

A common cause of non-accessible web pages are elements that were made interactive via JavaScript but cannot be focused or activated with anything but the mouse.

❌ Bad example

Let's take a look at a common example:

<form filter>
  <input filter--query name="query" type="text">
  <span filter--reset>Clear Search</span>
</form>

The HTML above is being activated with an Unpoly compiler like this:

up.compiler('[filter]', function(filterForm) {
  const resetButton = filterForm.querySelec...

I recently built a screen with a very high and wide table in the center. This posed some challenges:

• Giving the table a horizontal scroll bar is very unergonomic, since the scrollbar might be far off screen.
• Making the whole page scrollable looks bad, since I don't want the rest of the UI to scroll.
• Giving the table its own vertical scrollbar and a limited height would have solved it, but felt weird, since the table was 90% of the page.

What I ended up doing is reusing the horizontal page scrollbar (which is naturally fixed at t...