HOWTOs for Ruby on Rails and JavaScript

Jasmine: Expecting objects as method invocation arguments

To check if a method has been called in Jasmine, you first need to spy on it:

let spy = spyOn(window, 'alert')
codeThatAlerts()
expect(window.alert).toHaveBeenCalledWith('Important message')

To expect an object of a given type, pass the constructor function to jasmine.any():

expect(spy).toHaveBeenCalledWith(jasmine.any(Object))
expect(spy).toHaveBeenCalledWith(jasmine.any(String))
expect(spy).toHaveBeenCalledWith(jasmine.any(Number))

To expect an object with given key/value properties, use `jasmine.objectContaining(...

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Firefox cancels any JavaScript events at a fieldset[disabled]

If you try to listen to events on elements that are nested inside a <fieldset disabled>, Firefox will stop event propagation once the event reaches the fieldset. Chrome and IE/Edge will propagate events.

Since we often bind event listeners to document this can be annoying.

You could solve it by...

...adding event listeners on elements themselves. Note that this is terrible when you have many elements that you'd register events for.
...adding event listeners on a container inside the <fieldset>, around your eleme...

jsbin.com

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HTML: Making browsers wrap long words

By default, browsers will not wrap text at syllable boundaries. Text is wrapped at word boundaries only.

This card explains some options to make browsers wrap inside a long word like "Donaudampfschifffahrt".

Option 1: hyphens CSS property (preferred)

Modern browsers can hyphenate natively. Use the hyphens CSS property:

hyphens: auto

There is also hyphens: none (disable hyphenations even at  entities) and hyphens: manual (hy...

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JavaScript: Testing the type of a value

Checking if a JavaScript value is of a given type can be very confusing:

There are two operators typeof and instanceof which work very differently.
JavaScript has some primitive types, like string literals, that are not objects (as opposed to Ruby, where every value is an object).
Some values are sometimes a primitive value (e.g. "foo") and sometimes an object (new String("foo")) and each form requires different checks
There are three different types for null (null, undefined and NaN) and each has different rules for...

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Spreewald: Content-Disposition not set when testing a download's filename

Precondition

You are not using javascript tests
The file is served from a public folder (not via controller)

Problem description

If you deliver files from a public folder it might be that the Content-Disposition header is not set. That's why the following spreewald step might raise an error:

Then I should get a download with filename "..."

expected: /filename="some.pdf"$/
     got: nil (using =~) (RSpec::Expectations::ExpectationNotMetError)

Solution

One solution...

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Fixing flaky E2E tests

An end-to-end test (E2E test) is a script that remote-controls a web browser with tools like Selenium WebDriver. This card shows basic techniques for fixing a flaky E2E test suite that sometimes passes and sometimes fails.

Although many examples in this card use Ruby, Cucumber and Selenium, the techniques are applicable to all languages and testing tools.

Why tests are flaky

Your tests probably look like this:

When I click on A
And I click on B
And I click on C
Then I should see effects of C

A test like this works fine...

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Async control flow in JavaScript: Promises, Microtasks, async/await

Slides for Henning's talk on Sep 21st 2017.

Understanding sync vs. async control flow

Talking to synchronous (or "blocking") API

print('script start')
html = get('/foo')
print(html)
print('script end')

Script outputs 'script start', (long delay), '<html>...</html>', 'script end'.

Talking to asynchronous (or "evented") API

print('script start')
get('foo', done: function(html) {
  print(html)
})
print('script end')

Script outputs 'script start', 'script end', (long ...

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How to exploit websites that include user input in their CSS

The linked article shows how to exploit websites that include unsanitized user input in their CSS.

Although the article often mentions React and CSS-in-JS libraries, the methods are applicable to any web app that injects user input into style tags or properties.

Also, sanitizing user input for CSS injection is much harder than sanitizing HTML.

reactarmory.com

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JavaScript bookmarklet to click an element and copy its text contents

Here is some JavaScript code that allows you to click the screen and get the clicked element's text contents (or value, in case of inputs).

The approach is simple: we place an overlay so you don't really click the target element. When you click the overlay, we look up the element underneath it and show its text in a browser dialog. You can then copy it from there.

While moving the mouse, the detected element is highlighted.

Here is the one-liner URL that you can store as a bookmark. Place it in your bookmarks bar and click it to activate....

gist.github.com

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Async/Await Will Make Your Code Simpler

Sometimes modern Javascript projects get out of hand. A major culprit in this can be the messy handling of asynchronous tasks, leading to long, complex, and deeply nested blocks of code. Javascript now provides a new syntax for handling these operations, and it can turn even the most convoluted asynchronous operations into concise and highly readable code.

blog.patricktriest.com

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JavaScript: Polyfill native Promise API with jQuery Deferreds

You should prefer native promises to jQuery's Deferreds. Native promises are much faster than their jQuery equivalent.

Native promises are supported on all browsers except IE <=11, Android <= 4.4 and iOS <= 7.

If you need Promise support for these old browsers y...

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JavaScript: How to query the state of a Promise

Native promises have no methods to inspect their state.

You can use the promiseState function below to check whether a promise is fulfilled, rejected or still pending:

promiseState(promise, function(state) {
  // `state` now either "pending", "fulfilled" or "rejected"
});

Note that the callback passed to promiseState will be called asynchronously in the next [microtask](https://jakearchibald.com/2015/tasks-microtasks-queues-and-schedules/...

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Caution when using the || operator to set defaults

I often see the use of || to set a default value for a variable that might be nil, null or undefined.

x = x || 'default-value'

This pattern should be avoided in all languages.

While using || works as intended when x is null or an actual object, it also sets the default value for other falsy values, such as false. false is a non-blank value that you never want to override with a default.

To make it worse, languages like JavaScript or Perl have [many more fal...

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Cucumber: Clear localStorage after each scenario

Capybara clears cookies before each scenario, but not other client-side data stores. If your app is using localStorage or sessionStorage, contents will bleed into the next scenario.

Use this hook to remove all site data after each scenario:

After do
  if Capybara.current_driver == :selenium && !Capybara.current_url.starts_with?('data:')
    page.execute_script <<-JAVASCRIPT
      localStorage.clear();
      sessionStorage.clear();
    JAVASCRIPT
  end
end

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How to make select2 use a Bootstrap 4 theme

select2 is a great jQuery library to make (large) <select> fields more usable.

For Bootstrap 3 there is select2-bootstrap-theme.
It won't work for Bootstrap 4, but rchavik's fork does (at least with Bootstrap 4 Alpha 6, current version at time of writing this).

It is based on a solution by angel-vladov and adds a few fixes.

Use it by addi...

select2-bootstrap4.png

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How to make Webpacker compile once for parallel tests, and only if necessary

Webpack is the future. We're using it in our latest Rails applications.

For tests, we want to compile assets like for production.
For parallel tests, we want to avoid 8 workers compiling the same files at the same time.
When assets did not change, we do not want to spend time compiling them.

Here is our solution for all that.

Its concept should work for all test suites.

Copy the following to config/initializers/webpacker_compile_once.rb. It will patch Webpacker, but only for the test environment:

# Avoid hardcoded asset host...

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Cucumber: Test that an element is not overshadowed by another element

I needed to make sure that an element is visible and not overshadowed by an element that has a higher z-index (like a modal overlay).

Here is the step I wanted:

Then the very important notice should not be overshadowed by another element

This is the step definition:

Then(/^(.*?) should not be overshadowed by another element$/) do |locator|
  selector = selector_for(locator)
  expect(page).to have_css(selector)
  js = <<-JS
    var selector = #{selector.to_json};
    var elementFromSelector = document.querySelector(selector)...

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Clicking issues with chromedriver

ChromeDriver clicking works by simulating a mouse click in the middle of the element's first client rect (or bounding client rect if it doesn't have a first client rect). (Clicking issues)

So if you are trying to click on an element, chromedriver tries to click at the position where it first finds that element.

This can lead to some problems and unexpected behavior like:

Element is not clickable at point ... erros
Another element which is now located at...

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Middleman configuration for Rails Developers

Middleman is a static page generator that brings many of the goodies that Rails developers are used to.

Out of the box, Middleman brings Haml, Sass, helpers etc. However, it can be configured to do even better. This card is a list of improvement hints for a Rails developer.

Gemfile

Remove tzinfo-data and wdm unless you're on Windows. Add these gems:

gem 'middleman-livereload'
gem 'middleman-sprockets' # Asset pipeline!

gem 'bootstrap-sass' # If you want to use Bootstrap

gem 'byebug'

gem 'capistrano'
gem 'capistrano-mid...

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ruby-sass: Do not use comments between selector definitions

Sass lets you easily specify multiple selectors at once like this:

.some-block
  &.has-hover,
  &:hover
    outline: 1px solid red

This will add a red outline on either real hover or when the has-hover class is present. However, adding a comment will void the definition of that line:

.some-block
  &.has-hover, // From hoverable.js <-- DON'T
  &:hover
    outline: 1px solid red

... will simply drop the &.has-hover part in ruby-sass(deprecated). [sassc](https://rubygems.org/g...

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JavaScript Coordinates

To move elements around we should be familiar with coordinates. Most JavaScript methods deal with one of two coordinate systems:

Relative to the window(or another viewport) top/left.

Relative to the document top/left.
It’s important to understand the difference and which type is where.

javascript.info

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JavaScript Start-up Performance

As web developers, we know how easy it is to end up with web page bloat. But loading a webpage is much more than shipping bytes down the wire. Once the browser has downloaded our page’s scripts it then has to parse, interpret & run them. In this post, we’ll dive into this phase for JavaScript, why it might be slowing down your app’s start-up & how you can fix it.

The article author also tested 6000+ production sites for load times. Apps became interactive in 8 seconds on desktop (using cable) and 16 seconds on mobile (Moto G4 over 3G).

medium.com

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How to get the currently selected text in Javascript

Simple:

window.getSelection().toString();

Browser support: IE9+, Android 4.3+, Safari 5+

stackoverflow.com

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JavaScript: Hash/Object with default value

You can easily have a JavaScript hash/object that returns a default value for unset keys/properties -- as long as you need to support only recent browsers.

The key are JavaScript proxies from ECMAScript 6 that allow implementing a custom getter method. They work like this:

var hash = new Proxy({}, {
  get: function(object, property) {
    return object.hasOwnProperty(property) ? object[property] : 'hello';
  }
});

When you set a key,...

developer.mozilla.org

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