Upgrade gems

You need to update a lof gems. Make sure you don't have any version constraints in your Gemfile or your bundle update won't do anything!

Upgrade cucumber_priority:

bundle update cucumber_priority

Upgrade spreewald:

bundle update spreewald

Upgrade cucumber_factory:

bundle update cucumber_factory

Upgrade parallel_tests:

bundle update parallel_tests

Even on the latest version, parallel_tests will print some deprecation warnings due to using an older formatter A...

jQuery doesn't store information about event listeners and data values with the element itself. This information is instead stored in a global, internal jQuery cache object. Every time you add an event listener or data value to a jQuery object, the jQuery cache gains another entry.

The only way that a jQuery cache entry gets deleted is when you call remove() on the element that put it there!

Since cache entries also have a pointer back to the element that spawned them, it is easy to create DOM elements that can never be garbage-co...

TLDR: This card explains which threads and processes interact with each other when you run a Selenium test with Capybara. This will help you understand "impossible" behavior of your tests.

When you run a Rack::Test (non-Javascript) test with Capybara, there is a single process in play. It runs both your test script and the server responding to the user interactions scripted by your test.

A Selenium (Javascript) test has a lot more moving parts:

1. One process runs your test script. This is the process you...

Although regular expression syntax is 99% interchangeable between languages, keep this in mind:

• By default, the dot character (".") does not match a line feed (newline, line break, "\n") in any language.
• Some languages allow you to modify the behavior of a regular expression by appending a modifier to the pattern expression. E.g. /foo/i makes the pattern case-insensitive in many languages. Note however that some of these modifiers may not exist or mean entirely different things in different languages.
• Some languages have a m...

tl;dr

In Chrome DevTools in the Elements tab or in Firefox in the Inspector tab you can right click on an element and choose Break on to debug changes related to this element.

Example

DOM Breakpoints can be quite useful to quickly find the JavaScript that is responsible for some (unexpected) behavior. You can use DOM Breakpoints for debugging subtree modifications, attribute modifications or node removal.

Here you can see a very simple example that shows what JavaScript lines are responsible for ...

Webpack builds can take a long time, so we only want to compile when needed.

This card shows what will cause Webpacker (the Rails/Webpack integration) to compile your assets.

When you run a dev server

While development it is recommended to boot a webpack dev server using bin/webpack-dev-server.

The dev server compiles once when booted. When you access your page on localhost before the initial compilation, the page may load without assets.

The ...

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...

Any form fields where users enter numbers should be an <input type="number">.

Numeric inputs have several benefits over <input type="text">:

• On mobile or tablet devices, number fields show a special virtual keyboard that shows mostly digit buttons.
• Decimal values will be formatted using the user's language settings.
  For example, German users will see 1,23 for <input type="number" value="1.23">.
• Values in the JavaScript API or when submitting forms to the server will always use a point as decimal separator (i.e. "1.23" eve...

tl;dr

We recommend configuring Selenium's unhandled prompt behavior to "ignore".

When running tests in a real browser, we use Selenium. Each browser is controlled by a specific driver, e.g. Selenium::WebDriver::Chrome for Chrome.

There is one quirk to all drivers (at least those following the W3C webdriver spec) that can be impractical:
When any user prompt (like an alert) is encountered when trying to perform an action, they will [dismiss the dialog by default](https://w3c....

When you allow file uploads in your app, a user might upload content that hurts other users.

Our primary concern here is users uploading .html or .svg files that can run JavaScript and possibly hijack another user's session.

A secondary concern is that malicious users can upload executables (like an .exe or .scr file) and use your server to distribute it. However, modern operating systems usually warn before executing files that were downloaded from t...

HTTP header values must only contain low-ASCII (7-bit) characters for safe transport. From RFC 7230:

Historically, HTTP has allowed field content with text in the ISO-8859-1 charset [ISO-8859-1], supporting other charsets only through use of [RFC2047] encoding. In practice, most HTTP header field values use only a subset of the US-ASCII charset [USASCII]. Newly defined header fields SHOULD limit their field values to US-ASCII octets.

If you need to transport 8-bit+ characters (e.g...

In a Jasmine spec you want to spy on a function that is imported by the code under test. This card explores various methods to achieve this.

Example

We are going to use the same example to demonstrate the different approaches of mocking an imported function.

We have a module 'lib' that exports a function hello():

// lib.js

function hello() {
  console.log("hi world")
}

export hello

We have a second module 'client' that exports a function helloTwice(). All this does is call hello() ...

Jasmine is a great way to unit test your JavaScript components without writing an expensive end-to-end test for every small requirement.

After we integrated Jasmine into a Rails app we often add an E2E test that opens that Jasmine runner and expects all specs to pass. This way we see Jasmine failures in our regular test runs.

RSpec

In a [feature spec](https://web.archive.org/web/20150201092849/http://www.rel...

You want to use <input type="number"> fields in your applications.
However, your desktop users may encounter some weird quirks:

1. Aside from allowing only digits and decimal separators, an "e" is also allowed (to allow scientific notation like "1e3").
   • Non-technical users will be confused by this.
   • Your server needs to understand that syntax. If it converts only digits (e.g. to_i in Ruby) you'll end up with wrong values (like 1 instead o...

When your Rails application server raises error, Capybara will fail your test when it clears the session after the last step. The effect is a test that passes all steps, but fails anyway.

Capybara's behavior will help you to detect and fix errors in your application code. However, sometimes your application will explode with an error outside your control. Two examples:

• A JavaScript library references a source map in its build, but forgets to package the source map
• CarrierWave cleans up an upload or cache file after the record was delet...

When you repeat a subpattern with a *, + or {...} operator, you may choose between greedy, lazy and possessive modes.

Switching modes may affect the result and performance of your regular expressions. In the worst case, an ill-suited mode may make your regular expression so slow that it can DoS your application (Examples are the ActiveRecord's PostgreSQL CVE-2021-22880 or the [Cloudflare outage 2019](https://makandracards.com/makandra/77515-regular-expressions-excessive-backtracking...

Scroll and touch event listeners tend to be computationally expensive as they are triggered very often. Every time the event is fired, the browser needs to wait for the event to be processed before continuing - the event could prevent the default behavior. Luckily there is a concept called passive event listeners which is supported by all modern browsers.

Below are the key parts quoted from WICG's explainer on passive event listeners. See [this demo video](https://www.youtube.com/watch?v=NPM6172...

When an event listener on a DOM element throws an error, that error will be silenced and not interrupt your program.

In particular, other event listeners will still be called even after a previous listener threw an error. Also the function that emitted the event (like element.dispatchEvent() or up.emit()) will not throw either.

In the following example two handlers are listening to the foo event. The first handler crashes, th...

RubyMine comes with a nice way to grep through your project's files: The finder (ctrl + shift + f). Don't be discouraged about the notice 100+ matches in n+ files if your searched keyword is too general or widely used in your project.

RubyMine comes with a few ways to narrow down the resulting list, don't hesitate to apply those filters to speed up your search. Your keybinding might vary based on your personal settings.

File mask (alt + k)

If you already know the file extension of your ...

Download buttons can be difficult to test, especially with Selenium. Depending on browser, user settings and response headers, one of three things can happen:

• The browser shows a "Save as..." dialog. Since it is a modal dialog, we can no longer communicate with the browser through Selenium.
• The browser automatically downloads the file without prompting the user. For the test it looks like nothing has happened.
• The browser shows a binary document in its own window, like a PDF. Capybara/Selenium freaks out because there is no HTML docum...

TL;DR Most web applications do not require action on this. SameSite=None (old browser default) will continue to work, and SameSite=Lax (new Chrome default, gradually rolled out) is an even better default for cookies. Set SameSite=Strict only for extra security in special cases (see below). If your application is rendered in an iframe (e.g. a video player or some news stream), you need to configure its relevant cookies as SameSite=None.

The SameSite cookie attribute targets **c...

HTML's <input type="file"> accepts a single file. You can allow multiple files via <input type="file" multiple>.
But sometimes, selecting multiple files is not enough and can be cumbersome for the user. Enter webkitdirectory:

<input type="file" webkitdirectory multiple>

Using webkitdirectory switches the browser's file picker to select a directory. All files inside that directory, and inside any nested subdirectories, will be selected for the file input.

This can be useful when users want to upload all files from a nested dire...