This document discusses using HTML5 Web Components to build reusable web components. It introduces several emerging Web Component standards including templates, imports, shadow DOM, and custom elements. Templates allow defining reusable DOM fragments, imports enable bundling HTML, CSS and JavaScript into a single component, shadow DOM provides DOM encapsulation, and custom elements define new semantic elements. While still in draft, Web Components aim to improve code reuse, encapsulation, separation of concerns and composition on the web. The presentation provides examples and demonstrations of each standard.

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

2. The Pyramid of Doom

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

4. 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

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

6. 1. Undescriptive Markup
Google+ Example

7. The Pyramid of Doom is
Back

8. 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!

9. 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>

10. 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?

11. 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

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

13. Let’s Drill Down

14. 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>

15. 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);

16. Demo
Templates

17. 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”>

18. 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

19. 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;

20. Demo
Imports

21. 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

22. Demo
Enabling Chrome to Show Shadow DOM Elements

23. 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>’;

24. Demo
Shadow DOM

25. 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’
});

26. 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>

27. Demo
Custom Elements

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

29. Questions?

30. 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!

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

32. Thank You!