Web Components.

Are we there yet?

live slides: goo.gl/ofHnzr

<video>

<h1>

<h2>

<h3>

<h4>

<h5>

<DIV>

<p>

<span>

<article>

<A>

<BODY>

<HEAD>

<STRONG>

<input>

<SELECT>

<TEXTAREA>

<IMG>

<UL>

<HTML>

<TITLE>

<meta>

<AUDIO>

<BUTTON>

<video>

<video width="480" controls poster="webmvp8.gif">
  <source src="webmvp8.webm" type="video/webm">
  <source src="webmvp8_512kb.mp4" type="video/mp4">
  <source src="webmvp8.ogv" type="video/ogg">
  Your browser doesn't support HTML5 video tag.
</video>

attributes

children elements

<VIDEO> HTML

<video> STRUCTURE

Internal structure

const video = document.createElement('video');
video.play();
video.pause();
video.addEventListener('loadedmetadata', ...);

methods

events

<video> DOM

video.controls = true;
video.poster = 'image.png';

properties

<video>

Inputs

Outputs

events

attributes
& properties

methods

play(), pause(),

etc...

src, poster, autoplay, etc..

internal DOM structure

canplay, pause, play, playing, ratechange, timeupdate, volumechange, error, etc...

<video> INTERFACE API

WHAT REALLY ARE
WEB COMPONENTS?

Four emerging specs

Custom Elements

Shadow DOM

Templates

HTML Imports

SHADOW DOM

Shadow DOM

Shadow DOM replaces element content with DOM subtree not directly connected to document.

ELEMENT

<p></p>

SHADOW DOM

ELEMENT

<p></p>

SHADOW DOM

<div>...

Shadow DOM

 Style rules are scoped. CSS selectors like id and class do not apply to elements outside.

ELEMENT

<style>
 #my-id { color: red }
</style>
<div id="my-id">
  Text
</div>

Shadow DOM

 Shadow DOM Slot API allows flexibly distribute content to Shadow DOM.

ELEMENT

<div id="wrapper">
  <slot name="title"></slot>
</div>

<slot></slot>

Shadow DOM API 

const div = document.createElement('div');

Or 'closed'

const shadowRoot = div.attachShadow({ mode: 'open' });
div.shadowRoot === shadowRoot  // For 'open' mode
shadowRoot instanceof DocumentFragment === true;

// We can add some content
shadowRoot.innerHTML = '<p>Some paragraph</p>';

div.children.length === 0; // true

CUSTOM ELEMENTS 

CUSTOM ELEMENTS 

Custom Elements API allows to define new elements.

<my-carousel swipe arrows>

  <my-carousel-item name="Item 1">
    <img src="image-1.png" />
  </my-carousel-item>

  <my-carousel-item name="Item 1">
    <img src="image-1.png" />
  </my-carousel-item>

</my-carousel>

CUSTOM ELEMENTS API 

class MyElement extends HTMLElement {
  constructor() {
    super();
    this.textContent = 'Sample text';
  }

  get something() { ... }
  
  myMethod() { ... }
}
customElements.define('my-element', MyElement);

CUSTOM ELEMENTS API

  • Attributes changes (attributeChangedCallback)
     
  • El. added to DOM (connectedCallback)
     
  • El. removed from DOM (disconnectedCallback)
     
  • El. moved to another document (adoptedCallback)

Google

standards

own standards

v33 (02/2014)

CUSTOM ELEMENTS V0

Shadow DOM V0

v25 (prefix) (02/2013), v35 (05/2014)

v40

in dev

v53

v10

in dev

Shadow DOM V1

v41

in dev

v54

in dev

in dev

Custom Elements V1

TEMPLATES

TEMPLATES

Templates declare fragments of DOM which can be activated later at runtime.

<template id="my-template">
  <h1>Title</h1>
  <img src="image.png" />
</template>

deferred request

TEMPLATES

Templates are implemented in every modern browser.

v15

v22

v26

v7.1

v13

HTML Imports

HTML Imports

HTML Imports are a way of including HTML documents in other documents.

<head>
  ...
  <link rel="import" href="bootstrap.html">
</head>

HTML Imports

HTML file may contains styles, templates, scripts, css, etc...

<link rel="stylesheet" href="bootstrap.css">
<script src="jquery.js"></script>
<script src="bootstrap.js"></script>
...

<template id="my-element">...</template>
<script> customElements.define(...) </script>
import 'bootstrap.css';
import jQuery from 'jquery';
import bootstrap from 'bootstrap';

const template = '...';

customElements.define(...);

HTML Imports

Mozilla and Webkit will not implement html imports in favor of ES6 Modules.

v23

v36

U/C

Web Components

Web Components

<MY-ELEMENT>

Inputs

Outputs

events

attributes
& properties

prototype methods

attributeChangedCallback,
prototype properties

Shadow DOM
+ Template

custom events dispatched on element
instance

WEB COMPONENTS.
IS IT WORTH?

My THOUGHTS

The most important specifications are shipped,
in development or can be polyfilled/shimmed.

Web components are great way to unify
creating UI libraries.

Web components will never replace JS frameworks.

Resources

Polymer

X-Tag

SkateJS

WebComponents.org

Custom Elements v1:
Reusable Web Components​

THANK YOU

Web Components. Are we there yet?

By Dominik Lubański

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Web Components. Are we there yet?

What really are web components? How they work? Can we use them today?

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