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Iasi code camp 12 october 2013 shadow dom - mihai bîrsan

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Iasi code camp 12 october 2013 shadow dom - mihai bîrsan

  1. 1. The Shadow DOM A Talk about Web Components in HTML5 Mihai Bîrsan October 2013
  2. 2. The Shadow DOM A Talk about Web Components in HTML5 Mihai Bîrsan October 2013
  3. 3. Previously... • Mutation Observers help observe changes in the DOM • The M in DOM is for Model • We can’t have models in the DOM
  4. 4. There is cruft in your HTML • Modern applications like GMail
  5. 5. There is cruft in your HTML • Frameworks like ExtJS
  6. 6. There is cruft in your HTML • HTML can be beautiful again –Readable –Meaningful • We can encapsulate presentation and behavior into components
  7. 7. Solutions from the future 1. Shadow DOM 2. HTML Templates 3. Custom Elements
  8. 8. Warning! • We’re about to talk about The Edge! • The Edge is bound to change rapidly • DO NOT use in production • Polyfills are available for the technologically impatient
  9. 9. 2. It’s nice to stamp out DOM TEMPLATES
  10. 10. Defining templates <template id="tweet-template"> <div class="tweet"> <img class="profile-picture" src="" alt="" /> <a class="author" href=""> <small class="shorthand"></small></a> <p class="tweet-content"></p> <a class="time-ago" href=""></a> </div> </template>
  11. 11. Like regular templates, but DOM • “inert” DOM tree: parsed but not interpreted –no images or stylesheets loaded –no scripts executed • can be cloned into to other nodes
  12. 12. Using templates via JS var t = document.querySelector('#tweet-template'); tweets.forEach(function (myTweet) { var tweetNode = t.content.cloneNode(true); populateNode(tweetNode, myTweet); document.body.appendChild(tweetNode); }); // t.innerHTML is also also available
  13. 13. Like regular templates, but DOM • Very efficient –cloning with nodes, not parsing –resources are loaded late, only when needed
  14. 14. 3. Bringing it home with CUSTOM ELEMENTS
  15. 15. Creating HTML elements • Registered via JavaScript var proto = Object.create(HTMLElement.prototype, { createdCallback: { value: function () { } } }); var MyElement = document.register('my-element', { prototype: proto }); • Must contain a dash in the name
  16. 16. Lifecycle callbacks method • createdCallback –an instance of the element is created • enteredViewCallback –an instance was inserted into the document • leftViewCallback –an instance was removed • attributeChangedCallback –an attribute of the node was added, removed, or updated
  17. 17. Working with custom elements • Can be instantiated declaratively <my-element></my-element> • or with JavaScript document.body.appendChild(new MyElement());
  18. 18. Extending HTML elements • Can also extend existing elements var MegaButton = document.register('mega-button', { prototype: Object.create(HTMLButtonElement.prototype) }); • Which is used like this <button is="mega-button"></button>
  19. 19. A brief note on FOUC • Flash of Unstyled Content • Unresolved HTML elements –that’s why they must contain a dash –target in CSS with :unresolved
  20. 20. 1. The most awesome and most important piece SHADOW DOM
  21. 21. What’s a Shadow DOM? • A tree of nodes attached to a host node, but is not a child • Meant to abstract away the presentation layer from it’s semantics
  22. 22. How does Shadow DOM work? • Through composition before layout and rendering • The shadow tree replaces all of the host’s content • The host’s children are pulled into the shadow tree
  23. 23. The two trees <!-- The main DOM tree --> <div class="tweet"> ▶#document-fragment <img class="profile-picture" src="https://si0.twimg.com/profile_images/2996456104/b <a class="author" href="https://twitter.com/SoVeryBritish">VeryBritishProblems <sm <p class="tweet-content">Watching with quiet sorrow as you receive a different hairc <a class="time-ago" href="https://twitter.com/SoVeryBritish/status/387912080327974 </div>
  24. 24. The two trees <!-- The Shadow DOM tree --> <div class="left-column"> <content select="img.profile-picture"></content> </div> <div class="right-column"><content></content></div> <div class="tools"> <button class="btn-reply">Reply</button> <button class="btn-retweet">Retweet</button> <button class="btn-fav">Favorite</button> </div>
  25. 25. The two trees .tweet .left-column .right-column content content .brn-reply .tweet-content .time-ago .profile-picture a.author .tools .btn-retweet .btn-fav
  26. 26. Styling in the shadow • You have control over whether styles from the host pass-through • You can also reset all styles at insertion points • You can also target specific selected nodes from the host with content:distributed(selector)
  27. 27. Adding Shadow DOM via JS createdCallback: { value: function () { // Create the shadow DOM var t = document.querySelector('#tweet-template'); this.shadowRoot = this.createShadowRoot(); this.shadowRoot.appendChild(t.content.cloneNode(true)); } }
  28. 28. ALTOGETHER NOW! WEB COMPONENTS
  29. 29. Web Components  Custom Elements + Shadow DOM + Templates = Web Components
  30. 30. Let’s model something 0
  31. 31. What’s the markup? <oracle-card> <name>Pacifism</name> <cost>1W</cost> <img class="illustration" src="img/Pacifism.jpg" alt="" /> <types>Enchantment</types> <subtypes>Aura</subtypes> <rules> <rule><shorthand>Enchant creature</shorthand></rule> <rule>Enchanted creature can't attack or block.</rule> </rules> <flavor>For the first time in his life, Grakk felt a little warm and fuzzy inside.</flavor> </oracle-card>
  32. 32. DEMO Well, you just had to be there... But for good measure, check my GitHub. I’ll post it there soon
  33. 33. In conclusion • The future of the web is awesome • With components we can encapsulate and separate presentation from content • Web components are much easier to reuse without inadvertent interference
  34. 34. You can use these things today! • Test the future of the web with Firefox Nightly and Chrome Canary • Add polyfills with Polymer to use web components in any browser
  35. 35. It’s that time when you ask me questions and I hand out prizes! THANK YOU! PLEASE FILL YOUR REVIEW FORMS!

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