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Introducing Web Components
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Peter Gasston
September 28, 2013
Technology
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Introducing Web Components
Front-end London one-day event, September 2013
Peter Gasston
September 28, 2013
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Transcript
Introducing Web Components #FELOneDay 09/13
Peter Gasston @stopsatgreen broken-links.com
Creative Technologist / Front-end lead rehabstudio.com
1. Subject to change 2. There will be code
Web Components
The secret of Ultimate Power!
{demo}
What The FrontEndLondon?
None
Shadow DOM
Rendered but invisible in the DOM.
None
Make your own Shadow DOM
Shadow Root DOM Host Cat Wars
Shadow root var newRoot = $(foo).createShadowRoot(), newEl = '<h2>Shadow world!</h2>';
newRoot.innerHTML = newEl;
<div id="foo"> <h1>Hello world!</h1> </div> Shadow root
<div id="foo"> <h1>Hello world!</h1> <h2>Shadow world!</h2> </div> Shadow root
{demo}
Shadow DOM <h1 /> <h2 /> <div id="foo"> Real DOM
Shadow DOM Shadow Host
A DOM hidden inside the DOM.
Ultimate Power!
A problem Shadow DOM
None
.foo { color: #00f; } The problem <div class="foo"> …
</div> div.foo { color: #f00; } <div class="foo"> … </div>
The Solution Encapsulation
Encapsulation 1. It has all it needs. 2. Nothing gets
in, nothing gets out.
Encapsulation 1. We run things, things don’t run we. 2.
Don’t take nothing from nobody.
<iframe src="foo.htm"> • Extra network requests • Multiple rendering contexts
• CORS conflicts • Generally a bit shit Encapsulation
Web Components Better encapsulation
a set of emerging standards aimed at making reusable widgets.
Web Components:
the biggest change to web dev since XMLHttpRequest. Web Components:
Shadow DOM Templates Custom elements
Shadow DOM Templates Custom elements
Shadow DOM Templates Custom elements
Mustache, etc. <script id="foo" type="text/template"> <h2>Hello world!</h2> </script>
The template element <template id="foo"> <h2>Hello world!</h2> </template>
The markup is inert.
The template element <template id="foo"> <script src="foo.js"></script> <img src="foo.png"> </template>
The template element <template id="foo"> <h2>Hello world!</h2> </template> Content
The content object var clone = $(foo).content.cloneNode(true), bar = document.getElementById('bar');
bar.appendChild(clone);
Templates <div id="bar"> <h1>#FELOneDay</h1> </div>
Templates <div id="bar"> <h1>#FELOneDay</h1> <h2>Hello world!</h2> </div>
The markup is active.
Templates + Shadow DOM var newRoot = $(foo).createShadowRoot(), clone =
$(bar).content.cloneNode(true), newRoot.innerHTML = clone;
The content element <template> <div> <h2>Hello world!</h2> <content></content> </div> </template>
<p>Good afternoon, London!</p> The content element <div> <h2>Hello world!</h2> </div>
Templates + Shadow DOM var newRoot = $(foo).createShadowRoot(), el =
document.createElement('content'); newRoot.innerHTML = el;
Templates
<link rel="import" href="tmpls.html"> HTML Imports
HTML Imports var lnk = 'link[rel="import"]', impt = document.querySelector(lnk), tpl
= lnk.import.getElementById('foo'), clone = tpl.content.cloneNode(true);
HTML Imports
Shadow DOM Templates Custom elements
Custom elements <div class="frontend"></div>
Custom elements document.register('front-end'); <front-end></front-end>
Custom elements + shadow DOM + templates <front-end></front-end>
Custom elements document.register('front-end', { extends: 'button' }); <button is="front-end">Go</button>
Custom element API var fe = Object.create( HTMLElement.prototype ); fe.foo
= function() { // Something }; document.register('front-end', { prototype: fe });
The element element <element name="front-end"> <template> <style scoped>…</style> <button> #document-fragment
<div>…</div> </button> </template> </element>
Fully encapsulated & reusable
Encapsulation Reusability Portability Shadow DOM Templates Custom elements
That’s basically it.
None
Appendix A: More about Encapsulation
The shadow boundary
The shadow boundary CSS & JS
The shadow boundary CSS & JS
Shadow root var shad = newRoot.shadowRoot; shad.querySelector('h2');
The shadow boundary CSS
.applyAuthorStyles newRoot = foo.createShadowRoot(); newRoot.applyAuthorStyles = true;
The shadow boundary CSS
Pseudo-elements
Pseudo-elements <progress> <div>::-webkit-progress-bar <div>::-webkit-progress-value
{demo}
The part attribute var newRoot = el.createShadowRoot(), newEl = '<h2
part="apes">…</h2>'; newRoot.appendChild(newEl);
Show me your parts <div class="foo"> #document-fragment <h2 part="apes">Shadow world!</h2>
</div> .foo::part(apes) { color: red; }
Appendix B: Scope
<p>Hello</p> <div> <style> p { color: #f00; } </style> <p>World!</p>
</div> <p>Again</p> Scoped styles
<p>Hello</p> <div> <style scoped> p { color: #f00; } </style>
<p>World!</p> </div> <p>Again</p> Scoped styles
css = '<style>p { color: #f00; }</style>'; newRoot.appendChild(css); Shadow scope
Custom properties
(don’t call them variables)
body { var-highlight: #f00; } Custom properties h1 { color:
var(highlight); }
Custom properties .foo { var-highlight: #00f; } body { var-highlight:
#f00; }
Custom properties <div class="foo"> #document-fragment <style> h1 { color: var(highlight);
} </style> </div> body { var-highlight: #f00; }
Almost done
Shadow DOM Shadow DOM API Templates HTML imports Custom elements
Scoped styles Custom properties Browser support
87 Polymer project Polymer project
Useful links polymer-project.org updates.html5rocks.com/tag/webcomponents plus.google.com/+EricBidelman mozilla.github.io/brick customelements.io
Peter Gasston @stopsatgreen broken-links.com