Linked contentRepeats

Generating test images on the fly via JavaScript

When you need test images, instead of using services like lorempixel or you may generate test images yourself. You can do this via JavaScript.

Here is an ES6 function that generates a simple SVG image and returns it as a data: URI. All browsers support SVG, and you can easily adjust it yourself.

function svgUri(text) {
  let svg = `
    <svg width="320" height="240" xmlns="">
      <rect x="0" y="0" width="320" height="240" style...

Checklist: Using Carrierwave in a Rails project

This checklist should help you to check edge cases that are not part of the default Carrierwave configuration.


Always convert and strip user-provided images to sRGB

Debugging image color profiles is hard. You can't trust your eyes in this matter, as the image rendering depends on multiple factors. At least the operation system, browser or image viewer software and monitor influence the resulting image colors on your screen.

When we offer our users the possibility to upload images, they will most likely contain tons of EXIF metadata and sometimes exotic color profiles like eciRGB. We want to get rid of the metadata, as it might contain sensitiv…


FileIO: Writing strings as Carrierwave uploads

When you have string contents (e.g. a generated binary stream, or data from a remote source) that you want to store as a file using Carrierwave, here is a simple solution.

While you could write your string to a file and pass that file to Carrierwave, why even bother? You already have your string (or stream).
However, a plain StringIO object will not work for Carrierwave's ActiveRecord integration:

>> Attachment.create!(file:
TypeError: no implicit conversion of nil into String

This is because Carrierwave ex…


Common mistakes when storing file uploads with Rails

1. Saving files to a directory that is not shared between deploys or servers

If you save your uploads to a made up directory like "RAILS_ROOT/uploads", this directory goes away after every deploy (since every release gets a new). Also this directory is not shared between multiple application servers, so your uploads are randomly saved to one local filesystem or another. Fixing this afterwards is a lot of fun.

Only two folders are, by default, shared between our application servers and deployments: "RAILS_ROOT/storage" and `"RAILS…

Understanding grid sizes of (SVG) icons

A primer on vector graphics

For rastered image formats like JPG or PNG, each pixel is basically drawn on a fixed size canvas. To display such an image in a different size (say: 1.5 times larger than original), the renderer (your Browser / GPU / Monitor) needs to interpolate the color values of missing pixels. The image will appear slightly blurred.

This is different for vector graphics like the SVG (Scalable Vector Graphics) format. You can imagine SVG files as XML file contai…

Linked contentRepeats

Ruby: Do not mix optional and keyword arguments

Writing ruby methods that accept both optional and keyword arguments is dangerous and should be avoided. This confusing behavior will be deprecated in Ruby 2.7 and removed in Ruby 3, but right now you need to know about the following caveats.

Consider the following method


def colored_p(object = nil, color: 'red')
puts object.inspect

colored_p(['an array']) # ['an array'] (in red)
colored_p({ a: 'hash' }, color: 'blue') # {:a=>'hash'} (in blue)
colored_p({ a: 'ha…

A collection of useful design resources for developers

This collection contains some useful design resources for developers. Many of them were mentioned in the Refactoring UI tutorials.




Using CSS transitions

CSS transitions are a simple animation framework that is built right into browsers. No need for Javascript here. They're supported by all browsers.

Basic usage

Transitions are used to animate the path between to property values. For example, to let the text color fade from red to green on hover, the following SASS is used (shorthand syntax):

  color: red
  transition: color .1s
    color: green

This tells the browser "whenever the color of an .element changes…

Linked contentDeprecated


Richard Powell presents a collection of CSS styling advice that's mainly taken from SMACSS. Although at makandra we're using BEM instead of SMACSS, here's my favorites.

Do not use ID's in CSS Selectors

It is never safe to assume there will only ever be one of something on a page so do not use ID's for CSS. Id's are much better used as javascript hooks so use them for this instead.

.list {…} instead of #list {…}

Animate an interface using classes not inline styles

Inline styles added by javascript are h…

Linked content

Powerful favicon generator

This favicon generator will guide you to a perfect set of favicon files, suitable for all devices and situations (browser, homescreen icon for iOS/Android/Windows, MacBook Touch Bar etc.)

How to

Open the Favicon generator and upload a square image:

  • either an SVG
  • or a PNG/JPG/… with more than 260px size

Then follow the steps it guides you. In the result window, stick to the HTML5 tab. It is just fine.


Joining PDFs with Linux command line

There are several ways to merge two (or more) PDF files to a single file using the Linux command line.

If you're looking for graphical tools to edit or annotate a PDF, we have a separate card for that.


The pdfjoin binary from pdfjam is probably already installed on your system. Usage:

pdfjoin one.pdf two.pdf --outfile out.pdf

Pages from joined documents might be rotated. To avoid this, call it like this:

pdfjoin one.pdf two.pdf --outfile out.pdf --paper a4paper --rotateoversize false



Controlling how your website appears on social media feeds

When a user shares your content, a snippet with title, image, link and description appears in her timeline. By default social networks will use the window title, the first image, the current URL and some random text snippet for this purpose. This is often not what you want.

Luckily Facebook, Twitter, etc. lets you control how your content appears in the activity streams. They even have agreed on a common format to do this: OpenGraph <meta> tags that go into your HTML's <head>:

<meta property="og:url" content="http://start.makan...

Regex: Be careful when trying to match the start and/or end of a text

Ruby has two different ways to match the start and the end of a text:

  • ^ (Start of line) and $ (End of line)
  • \A (Start of string) and \z (End of string)

Most often you want to use \A and \z.

Here is a short example in which we want to validate the content type of a file attachment. Normally we would not expect content_type_1 to be a valid content type with the used regular expression image\/(jpeg|png). But as ^ and $ will match lines, it matches both content_type_1 and content_type_2. Using \A and \z will wo…


CSS: Don't target multiple vendor-prefixed pseudo-elements in a single rule

Some pseudo-elements need to be addressed with vendor prefixes. E.g. ::selection is not supported by Firefox, you need to use ::-moz-selection instead.

What you cannot do is to define a single CSS rule to address both the standard and vendor-prefixed form:

::selection, ::-moz-selection {
  background-color: red;

This rule will be ignored by all browsers. The reason is that if a browser doe…


Webpack(er): A primer

webpack is a very powerful asset bundler written in node.js to bundle (ES6) JavaScript modules, stylesheets, images, and other assets for consumption in browsers.

Webpacker is a wrapper around webpack that handles integration with Rails.

This is a short introduction.


If you haven't already, you need to install node.js and Yarn.

Then, put

gem 'webpacker', '~> 4.x' # check if 4.x is still cu…

Adding Jasmine JavaScript specs to a Webpack(er) project

The goal is to get Jasmine specs running in a Rails project using Webpacker, with the browser based test runner. Should be easily adaptable to a pure Webpack setup.


Step 1: Install Jasmine

yarn add jasmine-core

Step 2: Add two separate packs

Since we do not want to mix Jasmine into our regular Javascript, we will create two additional packs. The first only contains Jasmine and the test runner. The second will contain our normal application code and the specs themselves.

We cannot…

Linked contentDeprecated Super-simple favicon generator

Eduardo Russo was tired of complex favicon creation and created his own favicon generator. It's really easy and allows a lot of image editing before rendering the favicons, in all needed sizes, formats and with the HTML needed to include them!

In Rails applications with Haml:

  • put all the favicon files into /public
  • store the HTML to app/views/layouts/_favicon.html
  • add = render 'layouts/favicon' to <head> in your application layout(s)

… and you're all…

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