Error handling in DOM event listeners

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...


Webpacker: Configuring browser compatibility

Webpacker uses Babel and Webpack to transpile modern JavaScript down to EcmaScript 5. Depending on what browser a project needs to support, the final Webpack output needs to be different. E.g. when we need to support IE11 we can rely on fewer JavaScript features. Hence our output will be more verbose than when we only need support modern browsers.

Rails 5.1+ projects often use Webpacker to preconfigure the Webpack pipeline for us. The default configuration works something like this:

  1. Webpack checks w...

You don't need each, collect or select in Coffeescript

Working with lists in Javascript is painful because the native Array class is so poorly designed.

One way to reduce the pain is to to use Underscore.js's functions like _.each, or, which unfortunately clutters your code with awkward calls to the _ helper.

Fortunately when you use CoffeeScript you don't need any of that. CoffeeScript has a very versatile for keyword that can do anything that each, collect or select can do. Enjoy!


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Rails: Including HTML in your i18n locales

TL;DR Append your locale keys with _html to have them marked as html_safe.

When you're localizing a Rails application, sometimes there is this urge to include a little HTML. Be it some localized link, or a set of <em> tags, you'd like to have it included in the locale file. Example:

# Locale file
    text: 'Please visit our <a href="">corporate website</a> to learn more about <em>the corporation</em>.'
= t('.text')
# Desired output
Please visit our <a href="https://w...

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: Soft hyphens

Unicode has a soft hyphen character you can use to mark optional word division opportunities. The soft hyphen is an invisible character with zero width. Only when the browser decides to wrap at a soft hyphen, it is turned in...

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Lazy-loading images

Since images are magnitudes larger in file size than text (HTML, CSS, Javascript) is, loading the images of a large web page takes a significant amount of the total load time. When your internet connection is good, this is usually not an issue. However, users with limited bandwidth (i.e. on mobile) need to mine their data budget better.

One popular strategy to improve the website performance is to not load images until they enter the viewport – aka "lazy-loading images".

General Issues

  • Crawlers do not execute JavaScript (generally sp...

How to evaluate CSS media queries in JavaScript

To make CSS rules dependent on the screen size, we use media queries:

@media (max-width: 500px) {
  // rules for screen widths of 500px or smaller

Browsers will automatically enable and disable the conditional rules as the screen width changes.

To detect responsive breakpoints from JavaScript, you may use the global matchMedia() function. It is supported in all brow...

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Updated: Five years of "Today I Learned" from Josh Branchaud

Added favorite TILs for Chrome, Git, and JavaScript. See bottom of that card.


PSA: "index: true" in Rails migrations does not work as you'd expect

Several Rails migration methods accept index: true as an option to create an index. In some cases (like #add_column), this option is silently discarded. Know what you are doing, or use #add_index instead.


Consider the following migration.

class CreateExamples < ActiveRecord::Migration
  def change
    create_table :examples do |t|
      t.references :category, index: true
      t.boolean :positive, index: true
      t.integer :number_of_participants, index: true


Jasmine: Testing AJAX calls that manipulate the DOM

Here is a Javascript function reloadUsers() that fetches a HTML snippet from the server using AJAX and replaces the current .users container in the DOM:

window.reloadUsers = ->
  $.get('/users').then (html) ->

Testing this simple function poses a number of challenges:

  • It only works if there is a <div class="users">...</div> container in the current DOM. Obviously the Jasmine spec runner has no such container.
  • The code requests /users and we want to prevent network interaction in our unit test...
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Five years of "Today I Learned" from Josh Branchaud

The linked GitHub repository is a bit like our "dev" cards deck, but groomed from a single person (Josh Branchaud). It includes an extensive list of over 900 TILs on many topics that might be interesting for most of us. (e.g. Ruby, Rails, Git, Unix..)


Here is an excerpt of all the Ruby TILs that were new to me. I encourage you to take your time to skim over the original list as well!


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('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('script end')

Script outputs 'script start', `'...


Always disable autocomplete for date pickers

When we write a form with date fields, we often use graphical data picker like Rome to get a consistent calendar popup on all browsers.

When you integrate a date picker popup, remember to also set autocomplete="off" on the text input that opens the calendar on click. Otherwise the autocomplete suggestions will cover the calendar box and make it unusable:


If you are using a tool like Unpoly you might want to set autocomplete="off" i...


Operators "in" and "of" are very inconsistent between CoffeeScript and JavaScript

CoffeeScript and JavaScript (ECMAScript) both have operators in and of. Each language use them for more than one purpose. There is not a single case where the same operator can be used for the same purpose in both languages.

Check if an object (or its prototype) has a property


var hasFoo = 'foo' of object


var hasFoo = 'foo' in object;

Iterate through all properties of an object


Redirecting responses for PATCH or DELETE will not redirect with GET

Redirect responses to PATCH and DELETE requests will be followed with PATCH or DELETE. Redirect responses to GET and POST will be followed with a GET.
The Rails form_for helper will use a workaround to send POST requests with a _method param to avoid this issue for PATCH/DELETE.

If you make requests yourself, watch out for the following behavior.

When you make an AJAX request PATCH /foo and the /foo action redirects to /bar, browsers will request PATCH /bar. You probably expected the second request to be...


Hilfe, ich hänge beim Programmieren fest!

Bei makandra bist Du mit Kollegen umgeben, die seit Jahren mit einem ähnlichen Stack entwickeln wie du. Es sollte deswegen nie einen Grund geben, länger allein an einem Programmierproblem festzuhängen.

In diesen drei Schritten kommst du immer und zeitnah zu einer Lösung:

  1. Dein Problem besser kennen lernen
  2. Gute Fragen in #geeks stellen
  3. Eskalation in #sos

Schritt 1: Dein Problem besser kennen lernen

Grenze das Problem ein

Ein erster Schritt bei der Problemsuche ist immer, den Ort im Quelltext einzugrenzen, der das unge...

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Event order when clicking on touch devices

Touch devices have their own set of events like touchstart or touchmove. Because mobile browsers should also work with with web applications that were build for mouse devices, touch devices also fire classic mouse events like mousedown or click.

When a user follows a link on a touch device, the following events will be fired in sequence:

  • touchstart
  • touchend
  • mousemove
  • mousedown
  • mouseup
  • click

Canceling the event sequence

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