Web components the future is here

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Web Components - The Future is
Here
Gil Fink
CEO and Senior Consultant, sparXys

The Pyramid of Doom

About Me
• sparXys CEO and Senior consultant
• ASP.NET/IIS Microsoft MVP
• Co-author of Pro Single Page Application
Development (Apress)
• Co-author of 4 Microsoft Official Courses (MOCs)

Agenda
• The problems we face
• Web Components APIs
o Templates
o Imports
o Shadow DOM
o Custom Elements
• Libraries to the rescue

1. Undescriptive Markup
Markup Example

2. Poor Separation of
Concerns
You want HTML, CSS and
JavaScript to work together
You end up with a mess
The wiring gets in your way!

3. No Native Templates
• Store HTML in hidden DOM element and show it
• Use script tag as a template holder:
<script id=”myTemplate” type=”text/template”>
<div>
…
</div>
</script>

4. No Bundling
• You want to bundle a complex component
The component includes HTML, CSS and JavaScript
how would you do that?
o Use a server side wrapping mechanism?

Web Components to the
Rescue
• A set of standards designed to componentize the
web
• Some general goals:
Code Reuse Encapsulation
Separation of
Concerns
Composition Theming Expressive Semantic

The Web Components
Standards
•Reusable DOM fragmentsTemplates
•Load HTML declarativelyImports
•DOM encapsulationShadow DOM
•Create your own elements
Custom
Elements

Setting The Environment
• Browsers have only partial support for Web
Components
o So we use the webcomponents.js Polyfill for Web Components
• Download:
o https://github.com/webcomponents/webcomponentsjs/
o Or install using your favorite package manager (Bower, Nuget)
• Make sure the Polyfill script runs first

Demo
Setting the environment

Let’s Drill Down

Templates
• A new HTML element – template
• Can be used to instantiate document fragments
• Can wrap HTML, style tags and script tags
• No data binding support 
• To use the template you need some JavaScript
magic
<template id=”myTemplate”>
<div>
…
</div>
</template>

Cloning a Template
• Select the template and extract its content
o Using its content property
• Use the importNode function to get the cloned
content
• Only when the clone is appended to the DOM
o The style and JavaScript are executed
o Resources like images are retrieved from the server
var template = document.querySelector(‘#myTemplate’);
var clone = document.importNode(template.content, true);

Templates
Demo

Imports
• Load additional HTML documents
o Without Ajax
• A new type of link tag
• Use the rel attribute with the import type:
<link rel=”import” href=”myImport.html”>

Imports and Bundling
• Enable to bundle a full component into one HTML
file
o The HTML can include scripts and CSS styles
• The whole bundle can be retrieved in a single call

Imports and The DOM
• Importing a document doesn’t include it into the
DOM
o It will parse it in memory and load all the additional resources
• Use the import property of the link tag:
var content = document.querySelector(‘link[rel=”import”]’).import;

Imports
Demo

Import Additional Notes
• Scripts running inside the import can reference the
containing document by calling
document.currentScript.ownerDocument
• CORS constraints apply to documents imported
from other domains

Shadow DOM
• Encapsulate DOM parts
o The browser will know how to present those parts
o The browser won’t show the encapsulated parts in the source code
• Creates a boundary between the component and
its user

The Problems Shadow
DOM Tries to Solve
• Encapsulation of components/widgets
• Style leakage
o Leaks from one component to another
o Leaks from imported 3th party library/framework
• Global DOM
o id or class attributes all over the place

Shadow DOM in The
Browser
<video src="media/myVideo.mp4" controls></video>
<input type="date">

Show Shadow DOM
Elements in Chrome
Demo

Shadow DOM – Cont.
• Use the createShadowRoot function to wrap an
element as a shadow DOM:
var host = document.querySelector(‘#shadowDOMHost’);
var root = host.createShadowRoot();
root.innerHTML = ‘<div>Lurking in the shadows</div>’;

Styling Shadow DOM
• :host and :host() pseudo-class
• ::content pseudo-element
<div name="myElement">
<style>
:host {
border: 1px solid lightgray;
}
</style>
<template>...</template>
</div>

Shadow DOM
Demo

Custom Elements
• Enable to extend or to create custom HTML
elements
o The new element must inherit from HTMLElement
• Create a custom element using the registerElement
function:
• Extend an existing element:
var myElement = document.registerElement(‘my-element’);
var myInput = document.registerElement(‘my-input’, {
prototype: Object.create(HTMLInputElement.prototype),
extends: ‘input’
});

Custom Elements –
Naming
• You can create named elements (almost) any way
you want:
o Same naming rules as other HTML tags
o There must be a dash (“-”) in the name
• To future-proof the name against the HTML standard
• To avoid naming collisions

Custom Elements – Usage
• Use the element in your DOM:
or use the createElement function:
<my-input></my-input>
var elm = document.createElement(‘my-input’);

Custom Element
Callbacks
• Custom elements have life cycle events:
• createdCallback
o Called when an instance is created
• attachedCallback
o Called when an instance is added to DOM subtree
• detachedCallback
o Called when an instance is removed from a DOM subtree
• attributeChangedCallback
o Called after an attribute value changes

Custom Elements
Demo

The Current State of Web
Components
• Still W3C Working Drafts
• Browser support:
http://caniuse.com/#search=web%20components
• Main libraries:
Polymer X-Tag

Polymer
• Components library that is written and maintained
by Google
• Includes
o Ability to build your own custom components
o Ready to use web components
• Polymer leverages the web components standard

Polymer Catalog
• Full catalog that includes various ready to use
components
• You can look at the component categories here:
https://elements.polymer-project.org/
• Support to Google material design and Google API
components included

Creating Custom
Elements in Polymer
<dom-module id="contact-card">
<link rel="import" type="css" href="contact-card.css">
<template>
<content></content>
<iron-icon icon="star" hidden$="{{!starred}}"></iron-icon>
</template>
<script>
Polymer({
is: 'contact-card',
properties: {
starred: Boolean
}
});
</script>
</dom-module>

Using The Custom
Elements in Polymer
<contact-card starred>
<img src="profile.jpg" alt="Gil's photo">
<span>Gil Fink</span>
</contact-card>

Polymer
Demo

X-Tag
• Components library that is supported by Microsoft
• Includes only the ability to write your own custom
components
o Ready to use web components can be found in the Brick library
• X-Tag leverages the web components standard

Creating Web
Components in X-Tag
xtag.register('x-myelement', {
lifecycle: {
created: function(){
// do something when the element is created
}
},
events: {
focus: function(){
// do something when the element in focus
}
},
methods: {
someMethod: function(){
// implementation
} }
});

X-Tag
Demo

Questions?

Summary
• Web Components are emerging standards that
enables:
• Encapsulation
• Separation of Concerns
• Element portability
• And more
• They are still in development
• Taking the web one step forward!

Resources
• Download the slide deck:
http://bit.ly/1OCOnbL
• http://webcomponents.org/
https://www.polymer-project.org/1.0/
http://www.x-tags.org/
• My Blog – http://www.gilfink.net
• Follow me on Twitter – @gilfink

Thank You!

Web components the future is here

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