To set a default Node version for new shells, use nvm alias default <VERSION>:

nvm alias default 1.2.3

I like to use the most recent LTS version as my default:

nvm alias default lts/erbium

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)
    expect(result).toEqual(jasmine.any(Number))
  })
})

Also see Expecting objects as method invocation arguments.

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...

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.

jQuery is still a useful and pragmatic library, but chances are increasingly that you’re not dependent on using it in your projects to accomplish basic tasks like selecting elements, styling them, animating them, and fetching data—things that jQuery was great at. With broad browser support of ES6 (over 96% at the time of writing), now is probably a good time to move away from jQuery.

[Practical and clear reference with the most common jQuery patterns and their equivalent translations in vanilla JS](https://tobiasahlin.com/blog/move-from-j...

Capybara provides execute_script and evaluate_script to execute JavaScript code in a Selenium-controlled browser. This however is not a good solution for asynchronous JavaScript.

Enter evaluate_async_script, which allows you to execute some asynchronous code and wait until it finishes. There is a timeout of a couple of seconds, so it will not wait forever.

Use it like this:

page.evaluate_async_script(<<~JS)
  let [done] = arguments
  doSomethingAsynchronous().then(() => {
    done() // call this to indicate we're done
  })
J...

WProofreader is a spelling and grammar checking tool that integrates with textareas and numerous WYSIWYG editors.
While it usually activates automatically, depending on your application, it may fail to boot.

In my case, an application was using CKEditor 4 and programmatically activated CKEditor. WProofreader's autoSearch logic failed to hook into that for some reason.

You can choose not to use its autoSearch feature, but explicitly enable WProofreader.
Here is a guide for CKEditor 4. It should apply to other WYSIWYG editors as well.

1...

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):

.element
  color: red
  transition: color .1s
  
  &:hover
    color: green

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

General hints on the DOM

• the root of the DOM is document
• custom elements inherit from HTMLElement. They need a - (dash) in their name, e.g. <notification-box>.
• event listeners don't have event delegation à la .on('click', cssSelector, handler)

Comparison

When an AJAX request raises an exception on the server, Rails will show a minimal error page with only basic information. Because all Unpoly updates work using AJAX requests, you won't get the more detailled better_errors page with the interactive REPL.

Below is an event listener that automatically repeats the request as a full-page load if your development error shows an error page. This means you get...

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.

Installation

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...

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 ...

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...

In Ruby on Rails, all objects have a useful blank? method. It returns true for nil but also for empty strings or empty arrays. There is also a universal method present? which returns true for all values that are not blank?.

In JavaScript you need to roll your own implementation of blank? and present?.

If your application uses [Unpoly](...

Not all versions of Node.js are compatible with each other. Also npm packages may require a minimum or maximum version of Node.js. We use nvm on our development PCs so we can operate multiple versions of Node.js in parallel.

To make sure that all developers use a compatible version of Node.js, your Rails project should declare the required Node.js in a file called .nvmrc.

When a .nvmrc exists, developers can cd in your project directory and activate...

jQuery has a function $.fn.trigger(). You can use it to dispatch an event on a jQuery object:

let $element = $('.foo')
$element.trigger('change')

A caveat is that such an event will be received by jQuery event listeners, but not by native event listeners:

let $element = $('.foo')

$element.on('change', event => console.log('I will be called'))
$element[0].addEventListener('change', event => console.log("I WON'T be called"))

$element.trigger('change')

This is not an issue when your entire app is ...

It is quite easy to migrate from CoffeeScript to ES6. You can use decaffeinate to convert your CoffeeScript source to modern JavaScript.

Install decaffeinate globally:

npm install -g decaffeinate

Call decaffeinate on each .coffee file, relaxing some options to get the most modern (and concise) JS:

decaffeinate file.coffee --use-cs2 --loose --optional-chaining --logical-assignment

Tip

If you use Babel and see errors while decaffeinati...

To keep JavaScript sources small, it can sometimes make sense to split your webpack bundles. For example, if your website uses some large JavaScript library – say TinyMCE – which is only required on some selected pages, it makes sense to only load that library when necessary.

In modern webpack this is easily doable by using the asynchronous import function.

Say we have an unpoly compiler that sets up TinyMCE like this (code is somewhat simplified):

// TinyMCE as part of the main bundle!

import tinymce from 'tinymce/tinymce'

// U...

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...

We're always striving towards keeping our website's JavaScript as small as possible.

If you're using webpack(er), you can use the webpack-bundle-analyzer plugin to get a good overview, which of your JavaScript modules take up how much space, and where you can optimize.

To use it, add it via npm or yarn

yarn add webpack-bundle-analyzer

Then add this to your environment.js:

// Uncomment this code to show statistics of bundle sizes. Generated file will automatically...