Build Reusable Web Components using HTML5 Web cComponents

Build Reusable Web Components
Using HTML5 Web Components
Gil Fink
CEO and Senior Consultant, sparXys

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)
• Founder of Front-End.IL Meetup and co-organizer of
GDG Rashlatz Meetup

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

1. Undescriptive Markup
Google+ 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

Templates
• A new HTML element – template
• Can be used to instantiate document fragments
• Can wrap HTML, style tags and script tags
• 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);

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 a 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;

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

Demo
Enabling Chrome to Show Shadow DOM Elements

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>’;

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 – Cont.
• Use the element in your DOM:
or use the createElement function
• Custom elements have life cycle events.
For example:
o createdCallback
o attributeChangedCallback
<my-input></my-input>

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

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

Resources
• Download the slide deck:
• http://webcomponents.org/
• My Blog – http://www.gilfink.net
• Follow me on Twitter – @gilfink

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