Web Components and Modular CSS

Web Components and Modular CSS
@AndrewRota | CSS Dev Conf 2014

CSS Features
Encapsulation
Scope
Interfaces
Modularity

Modular CSS Patterns
BEM
SMACSS
Atomic CSS
OOCSS

BEM
/* Block */
.nav { }
/* Element */
.nav__item { }
/* Block with Modifier */
.nav--hidden { }
/* Element with Modifier */
.nav__item--current { }

SMACSS
/* Module */
.nav { }
/* Module with State */
.nav.is-current { }
/* Module with Semantic Element Selector */
.nav > h2 { }
/* Layout Style */
.l-inline { }

Web Components
Web Components usher in a
new era of web development
based on encapsulated and
interoperable custom elements
that extend HTML itself. - Polymer

Web Components APIs
Custom Elements
HTML Templates
HTML Imports
Shadow DOM

Custom Elements
<my-element>Hello World.</my-element>
var MyElement = document.registerElement('my-element', {
prototype: Object.create(HTMLElement.prototype)
});

HTML Templates
<template id="my-template">
<p>Hello World.</p>

<img src="example.jpg" alt="Example">
</template>
document.importNode(
document.getElementById('my-template').content,
true
);

HTML Imports
<link rel="import" href="/imports/my-component.html">

Shadow DOM
// Create Shadow Root
document.getElementById('my-element').createShadowRoot();
// Access Shadow Root
document.getElementById('my-element').shadowRoot;

User Agent Shadow DOM
<video src="#" controls></video>
0:00

User Agent Shadow DOM
<input type="date">
mm/dd/yyyy

Shadow DOM
Shadow DOM.
Light DOM.
<div id="my-first-element"></div><p>Light DOM.</p>
// Create Shadow Root
var s = document.getElementById('my-first-element').createShadowRoot
// Add Styles and Text
s.innerHTML += '<style>p { color: crimson; margin: 5px 0 5px 0;}</s.innerHTML += '<p>Shadow DOM.</p>';

Content Insertion Points
<div id="my-second-element">
<content></content>
</div>

Shadow DOM and <content>
Shadow DOM Start.
Hello!
Shadow DOM End.
<div id="my-second-element"><p>Hello!</p></div>
var s = document.getElementById('my-second-element').createShadowRoot
s.innerHTML += '<p>Shadow DOM Start.</p>';
s.innerHTML += '<style>p { color: crimson; margin: 5px 0; }</style>'
s.innerHTML += '<content></content>';
s.innerHTML += '<p>Shadow DOM End.</p>';

Into the Light
/* pseudo-class for host element*/
:host { }
/* functional pseudo-class, for host if it matches the selector argument :host() { }
/* functional pseudo-class, for host context that matches selector :host-context() { }
/* pseudo-element, for distributed notes rendered via a <content> ::content { }

Into the Dark
/* pseudo-element for shadow roots */
::shadow { }
/* combinator for selecting through shadow boundaries */
body /deep/ p { }
[/deep/] is basically a super-descendant
combinator.
- CSS Scoping Module Draft, Issue 6

Let's Write a Component
Hello world, I am a web component.
<link rel="import" href="../assets/hello-world.html">
<hello-world>I am a <strong>web component</strong></hello-world

<template id="hw">
<style>
::content strong { color: crimson; }
p { margin: 2px 20px 2px 0; }
:host { border: 1px solid FireBrick; display: block; margin-right
.hello { color: #91D4D; }
</style>
<p><span class="hello">Hello world</span>, <content></content
</template>

var importedDoc = document.currentScript.ownerDocument;
var elementPrototype = Object.create(HTMLElement.prototype);
elementPrototype.createdCallback = function() {
var template = importedDoc.getElementById('hw').content;
var clone = document.importNode(template, true);
this.createShadowRoot().appendChild(clone);
};
document.registerElement('hello-world', {prototype: elementPrototype

Can I Use???
Custom
Elements
HTML
Templates
HTML
Imports
Shadow
DOM
- - - -
- - - -
Flag - Flag Flag
X - X X
X X X X

When To Use Web Components?
Third Party Widgets?
Third Party UI Libraries?
Internal UI Libraries?
Web Component All the Things!?

Third Party Widgets
<google-map
latitude="29.954356"
longitude="-90.067863">
</google-map>

Third Party UI Libraries
CSS HTML JS
<paper-radio-group selected="css">
<paper-radio-button name="css" label="CSS"></paper-radio-button
</paper-radio-group>
<paper-slider value="10"></paper-slider>

Internal UI Libraries
<acme-corp--menu>
<acme-corp--menu-item>Home</acme-corp--menu-item>
<acme-corp--menu-item selected>About</acme-corp--menu-item>
<acme-corp--menu-item>Contact Us</acme-corp--menu-item>
</acme-corp--menu>
<acme-corp--login-form
ajax
url="login.php">
</acme-corp--login-form>

Web Component Everything??
<acme-corp--app>
<acme-corp--menu></acme-corp--menu>
<acme-corp--content></acme-corp--content>
<acme-corp--footer></acme-corp--footer>
</acme-corp--app>

Probably Not (and that's OK)
I don't ever see us going all in
on Custom Elements for every
possible thing ... Use native
elements and controls when
possible and supplement with
custom elements.
- Joshua Peek, Github Programmer

Small
Open for Extension
Documented
Unit Tested
Accessible
Responsive
Best Practices

Towards a Component Driven Web

Thanks!
Resources
- WebComponents.org
- Web Components: A Tectonic Shift for Web Development by Eric Bidelman
- Web Components by Jarrod Overson and Jason Strimpel
- Ten Principles for Great General Purpose Web Components
Colophon
This presentation was built with Shadow DOM, HTML Templates, HTML
Imports, and the Custom Elements <slide-show> and <slide-content>
using Web Component Slides.

Web Components and Modular CSS

Web Components and Modular CSS

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