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

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Updated: Reading and writing cookies in JavaScript

  • Clarified how reading cookies works
  • Added section about using libraries, including link to Cookies.js

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 ——————-…


Escape a string for transportation in a URL

To safely transport an arbitrary string within a URL, you need to percent-encode characters that have a particular meaning in URLs, like & or =.

If you are using Rails URL helpers like movies_path(:query => ARBITRARY_STRING_HERE), Rails will take care of the encoding for you. If you are building URLs manually, you need to follow this guide.


In Ruby, use CGI.escape:

=> "foo%3Dfoo%26bar%3Dbar"

Do not ever use URI.encode or …

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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...
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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…

Jasmine: Test that an object is an instance of a given class

To test that an object was constructed by a given constructor function, use jasmine.any(Klass):

describe('plus()', function() {
  it ('returns a number', function() {
    let result = plus(1, 2)

Also see Expecting objects as method invocation arguments.


Defining new elements for your HTML document

Browsers come with a set of built-in elements like <p> or <input>. When we need a new component not covered by that, we often build it from <div> and <span> tags. An alternative is to introduce a new element, like <my-element>.

When a browser encounters an unknown element like <my-element>, the browser will proceed to render <my-element>'s children. The visual rendering of your page will not be affected.

If you care about their HTML being valid, your new element should contain a dash character (-) to mark it as a *custom el…


Detect the current Rails environment from JavaScript or CSS

Detecting if a Javascript is running under Selenium WebDriver is super-painful. It's much easier to detect the current Rails environment instead.

You might be better of checking against the name of the current Rails environment. To do this, store the environment name in a data-environment of your <body>. E.g., in your application layout:

%body{'data-environment' => Rails.env}

Now you can say in a piece of Jav…


Fixing flaky integration tests

This card shows basic techniques for fixing a flaky integration test suite that sometimes passes and sometimes fails. "Integration test" is a test script that remote-controls a web browser with tools like Selenium WebDriver.

Although the examples in this card use 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
When I click on B
When I click on C
Then I should see effects of C

A test like this works fine most of t…


Heads up: JavaScript does not like big numbers

In a JavaScript console, type this:

> 9112347935156469760


This occurs because JavaScript uses double precision floats to store numbers.

So according to IEEE floating point definition only numbers between -(2^53 - 1) (-9007199254740991) and 2^53 - 1 (9007199254740991) can safely be represented in JavaScript.

Note that ECMAScript 6 will probably also offer [Number.MAX_SAFE_INTEGER](…

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Defining "partials" in pure HTML without additional rendering helpers

A while ago I tweeted a thread about how a small JavaScript snippet, one that can fit in a single tweet in fact, can be used to allow defining custom elements purely in HTML. This post will expand on the idea, show how the snippet works, and argue for why you might want to actually use this.

A nice trick that lets you define "partials" in HTML without any additional rendering technology on the server or client.


Be careful when using buttons without a "type" attribute

Be careful when using buttons without a type attribute, since browsers will consider them the default submit button of a form.

Suppose you have this form:

<form action="/save">
  <input type="text" />
  <button onclick="alert('Alert!')">Alert</button>
  <button type="submit">Save</button>

If you press the enter key inside in the text input, browsers will trigger the first button and show the alert.

To fix this, add a type="button" attribute to the first button.

Coffeescript: Caveat when cloning objects with fat-arrow methods

Coffeescript allows you to create classes whose methods are automatically bound to the correct this. You can do this by using a fat arrow:

class Person

  constructor: (name) ->
    @name = name

  sayHello: =>
    alert("Hello, I am #{@name}")

An important caveat is that when you clone such an object, all of its methods are still bound to the original instance:

eve = new Person("Eve")
eve.sayHello() # => "Hello, I am Eve"
bob = _.clone(eve) = "Bob"
bob.sayHello() # => "Hello, I am Eve"

I don't thin…

Minified JavaScript and CSS

JavaScripts and CSS should be minified for production use.

In Rails 3.1+ the asset pipeline will take care of this. Thus you're best off using an uncompressed version of your Javascript in development. Also load the non-minified versions of libraries. This way debugging will be easier and you will still get all the minification love once deployed.

In Rails 2.3 and 3.0 you should at least embed external JavaScript libraries in minified form, using something like JavaScript compressor.

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