HOWTOs for Ruby on Rails and JavaScript

JavaScript without jQuery

This is a presentation from 2019-01-21.

Summary

We want to move away from jQuery in future projects
Motivations are performance, bundle size and general trends for the web platform.
The native DOM API is much nicer than it used to be, and we can polyfill the missing pieces
Unpoly 0.60.0 works with or without jQuery

Is jQuery slow?

From: Sven
To: unpoly@googlegroups.com
Subject: performance on smartphones and tablets

Hello

I just used your framework in one project and must say,
I am really pleased with it -- but o...

0.37.0.png 0.50.0.png

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Auto-generating plain-text bodies for HTML e-mails in Rails apps

When building an application that sends e-mails to users, you want to avoid those e-mails from being classified as spam. Most obvious scoring issues will not be relevant to you because you are not a spammer.

However, your application must do one thing by itself: When sending HTML e-mails, you should include a plain-text body or tools like SpamAssassin will apply a significant score penalty. Here is how to do that automatically.

Add premailer-rails to your Gemfile and bundle.
Done! ...

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CSS: How to find out the rendered font in chrome

The rendered font often depends on the local font your system provides, therefore you often find a rule like below in the computed style for an element:

font-family: Menlo,Monaco,Lucida Console,Liberation Mono,DejaVu Sans Mono,Bitstream Vera Sans Mono,Courier New,monospace,serif

This means if your system has a font named Menlo, it will render the text with this font. Otherwise it will try Monaco and so on. For the last two fallback options the system is free to use any monospace font or if not present any serif font. At lea...

Screenshot_from_2018-12-06_10-05-52.png

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How to: Use Ace editor in a Webpack project

The Ace editor is a great enhancement when you want users to supply some kind of code (HTML, JavaScript, Ruby, etc).
It offers syntax highlighting and some neat features like auto-indenting.

For Webpack 3+

Integrate as described in the documentation. For example load ace Editor like this:

  function loadAceEditor() {
    return import(/* webpackChunkName: "ace" */ 'ace-builds/src-noconflict/ace').then(() => {
      return import(/* webpackChunkName: "ace" */ 'ace-builds/webpack-r...

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How to: expand an element's cover area beyond its container

Occasionally, your designer will hand you designs where elements break the layout's horizontal container width, like navigation buttons of a slider that should be at the left/right of the browser window, or simply by applying a background color that reaches until the left and right of the browser window.

In the past, we've done some horrible things to achieve that. Like margin: 0 -10000px plus overflow-x: hidden.
There is a much saner approach.

Consider the following markup:

<body>
  <div class="container">
    <div class="sec...

codepen.io

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How to access before/after pseudo element styles with JavaScript

Accessing pseudo elements via JavaScript or jQuery is often painful/impossible. However, accessing their styles is fairly simple.

Using getComputedStyle

First, find the element in question.

let element = document.querySelector('.my-element') // or $('.my-element').get(0) when using jQuery

Next, use JavaScript's getComputedStyle. It takes an optional 2nd argument to filter for pseudo elements.

let style = window.getComputedStyle(element, '::before')
let color = style.getPropertyValue('background-color...

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Does <html> or <body> scroll the page?

TL;DR: All modern browsers default to using the <html> element as the main document viewport. In CSS, prefer to set overflow properties to html (or :root).

Scrolling the main viewport with JavaScript

The browser's main document viewport is also scrollable by default. The element that corresponds to the main viewport is either <html> (document.documentElement) or <body> (document.body). Which one depends on the browser.

When you want to update the current `sc...

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Minify Font Awesome fonts with webpack

Font Awesome 5 is a comprehensive solution for vector icons on your website.

Originally, Font Awesome came as an icon font (plus stylesheets), but recently it can also be used as a pure JavaScript solution (which will render icons as inline <svg> tags), or even as SVG sprites.

All solutions have their pros and cons:

Icon font:

little CPU load (no JavaScript)
fonts are relatively large
1 extra HTTP request

Javascript + inline SVG:

higher CPU load (needs to watch the DOM via mutation observers to ad...

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Do not use "flex: 1" or "flex-basis: 0" inside "flex-direction: column" when you need to support IE11

Flexbox is awesome. Most of it even works in IE11, but flex: 1 won't work reliably in Internet Explorer.
This it because implicitly sets flex-basis: 0 which IE fails to support properly.

Example

Consider the following HTML and CSS.

<div class="container">
  <div class="child">
    foo
  </div>
  <div class="bar">
    bar
  </div>
</div>

.container {
  display: flex;
  flex-direction: column;
}

.child {
  flex: 1;
}

See it in action at Plunker.

Background

...

plnkr.co

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HTML forms with multiple submit buttons

Most forms have a single submit button that will save the record when pressed.

Sometimes a form needs additional submit buttons like "accept" or "reject". Such buttons usually attempt a state transition while updating the record.

To process a form with multiple buttons, your server-side code will need to know which button was pressed. To do so you can give each submit button a different [formaction] attribute. This will override the ...

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How to make changes to a Ruby gem (as a Rails developer)

At makandra, we've built a few gems over the years. Some of these are quite popular: spreewald (> 1M downloads), active_type (> 1M downloads), and geordi (> 200k downloads)

Developing a Ruby gem is different from developing Rails applications, with the biggest difference: there is no Rails. This means:

no defined structure (neither for code nor directories)
no autoloading of classes, i.e. you need to require all files yourself
no active_support niceties

Also, their scope...

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Chrome bug: Wrong stacking order when transitioning composited elements

Google Chrome has a subtle rendering bug that hits me once in a while. It usually occurs in sliders with HTML content.

The issue

When a slider contains a composited[1] element, the element will overlap any other element when sliding, being rendered as frontmost element. After the slider has settled, stacking order jumps back to normal.

It seems like Chrome is doing its compositing wrong. This doesn't happen in Firefox.

The cause

The issue only occurs if:

two elements A and B are nested inside an element C
A overlaps B (part...

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Introduction to Google Tag Manager (for web developers who know Google Analytics)

As a web developer, you know Google Analytics (GA). Probably you've dropped the GA snippet into more than one website, maybe you've even used its Javascript API to implement tracking at the event level.

Google Tag Manager (GTM) is a related tool, but on a higher level and thus with much more power. GTM is not a replacement for GA. Rather, it can make GA configurable without changing anything in the application's code base (and much more beyond, see below).

Only prefer GTM if the customer requests it, or if he is updating his tracking r...

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Designing HTML emails

The 90s are calling: they want their tables back. Unfortunately, you need them all for laying out your HTML emails.

Email client HTML rendering is way more scattered than browser HTML. While you might have a pretty good understanding of what features and patterns you can use to support all major browsers, I doubt anyone masters this craft for HTML email clients.

The only way to ensure your email looks good (acceptable, at least) in all mail clients, is to check it. Litmus is your go-to solution for this (see below). W...

litmus.com

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Logic in media queries

Here is how to model basic logic in media queries.

AND

With keyword and.

# Target viewport widths between 500 and 800px
@media (min-width: 500px) and (max-width: 800px)

OR

Comma-separated.

# Target viewport widths below 500 or above 800px
@media (max-width: 500px), (min-width: 800px)

NOT

Needs a little overhead with not all and.

# Target devices that can't hover
@media not all and (hover)

See CSS: Using interaction media detection on why you'd need this.

developer.mozilla.org

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CSS: Using interaction media detection to disable hover styles for devices that have no hover

Since late 2015, all major browsers (still excluding Firefox) support pointing device media queries. These can be used to distinguish e.g. coarse from fine pointers (e.g. finger vs mouse), or a device with hover support from one without (e.g. desktop with mouse vs tablet).

Motivation

When hover styles modify the DOM, most mobile devices activate the hover styles on first tap. A second tap is required to trigger a click. While this can be handy, at times it makes the UX worse.

Another issue with hover styles is that they tend to st...

caniuse.com

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RSpec: Expect one of multiple matchers to match

RSpec let's you chain a matcher with .or. The expectation will then pass if at least one matcher matches:

expect(color).to eq("red").or eq("green")

Real-world example

A real-world use case would be to test if the current page has a button with the label "Foo". There are many ways to render a button with CSS:

<input type="button" value="Foo">
<input type="submit" value="Foo">
<button>Foo</button>

We cannot express it with a single have_css() matcher, since we need the { text: 'Foo' } optio...

rspec.info

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Printing background color of elements

Browsers' printing methods usually don't print background colors. In most cases this is the desired behavior, because you don't want to spend tons of ink printing the background of a web page. But in some cases you want to print the background color of elements, e.g. bars of a chart. For those elements you need to set the following CSS styles:

-webkit-print-color-adjust: exact; /* Chrome and Safari */
color-adjust: exact; /* Firefox */

Another case is printing of white text. When removing background colors, chances are white text n...

developer.mozilla.org

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CSS: Using the current text color for other color properties

There is a kinda secret, yet well supported CSS feature called currentColor. It's like a special CSS variable that has been supported in almost all browsers for almost all time (see linked Caniuse).

Usage

The currentColor value can be used in CSS to indicate the current value of color should be used. A common use case is setting a border color:

a.ghost
  color: white
  border: 1px solid currentColor
  &:hover
    color: red // Border color will change as well

Note that in many cases, you can simply omit the color to ac...

caniuse.com

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When you want to format only line breaks, you probably do not want `simple_format`

For outputting a given String in HTML, you mostly want to replace line breaks with <br> or <p> tags.
You can use simple_format, but it has side effects like keeping some HTML.

If you only care about line breaks, you might be better off using a small, specialized helper method:

def format_linebreaks(text)
  safe_text = h(text)
  paragraphs = split_paragraphs(safe_text).map(&:html_safe)

  html = ''.html_safe
  paragraphs.each do |paragraph|
    html << content_tag(:p, paragraph)
  end
  html
end

Full di...

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Two CSS layouting techniques compared: Flexbox vs. Grid

CSS Flexbox has become extremely popular amongst front-end developers the last couple of years. This isn’t surprising, as it has made it a lot easier for us to create dynamic layouts and align content within containers.
However, there’s a new kid in town called CSS Grid, and it’s got a lot of the same capabilities as Flexbox. In come cases it’s better than Flexbox, while in other cases it’s not.

If you are to take one lesson from this article, let it be this one:

Flexbox is made for one-dimensional layouts and Grid is made for tw...

hackernoon.com

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Generating test images on the fly via JavaScript or Ruby

When you need test images, instead of using services like lorempixel or placehold.it you may generate test images yourself.

Here we build a simple SVG image and wrap it into a data: URI. All browsers support SVG, and you can easily adjust it yourself.
Simply set it as an image's src attribute.

JavaScript

Simple solution in modern JavaScript, e.g. for use in the client's browser:

function svgUri(text) {
  let svg = `
    <svg wid...

jsfiddle.net

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HTML5: disabled vs. readonly form fields

Form fields can be rendered as noneditable by setting the disabled or the readonly attribute. Be aware of the differences:

disabled fields

don’t post to the server
don’t get focus
are skipped while tab navigation
available for button, fieldset, input, select, textarea, command, keygen, optgroup, option

Browser specific behavior:

IE 11: text inputs that are descendants of a disabled fieldset appear disabled but the user can still interact with them
Firefox: selecting text in a disabled text field is no...

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Form letters with LibreOffice Writer

This is painful. Consider using Microsoft Office or switching careers. If you need to write < 20 letters consider doing it manually.

So you didn't listen and here it comes:

Ignore the Mail Merge Wizard. It will crash or destroy your document.
Export your addresses, recipient names, etc. as a .ods spreadsheet (.xls, .xlsx, .ods). Use any columns that work for you, but be consistent. I like to use one column for the address, one column for the salutation line.
Import the spreadsheet as an address book source: *Tools => Add...

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