Let’s start the Web Components

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Let’s start the Web Components k-kuwahara @kuwahara_jsri @clown0082 Oct 30, 2018 ʲαϙʔλʔζCoLabษڧձʳ

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About me const my_info = { Workplace: ‘Yumemi Inc’, Community: ‘Riot.js, Ionic, DIST’, Favorites: ‘npm k-kuwahara ’, PokemonGO: ‘TL38’ }

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github.com/riot

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Sorry... # Because of time, I don’t mention all the grammar of JavaScript.

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⚠Attention⚠ We verified this slide with Google Chrome. Please check other browsers by yourself.

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What is “Web Components” ? How to program Custom Elements Shadow DOM ES Modules Practical usage Agenda

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What is Web Components?

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…before that

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A bit of background

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Component-oriented framework of JavaScript

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⚙ ⚙

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⚙ ⚙ ❌

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Is there something that doesn’t depend on any libraries?

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any ⚙ ⚙ ⚙ ⚙

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What is “Web Components” ?

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Works on “modern” browser

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No libraries required ❗ No packages required ❗ No modules required ❗

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No libraries required ❗ No packages required ❗ No modules required ❗ It doesn’t depend on tools or libraries

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ɹ Header Footer Navigation Bars (13 menus) Margen Sub Condition1 (list) Sub Condition2 (list) Main Condition2 (list) Main Condition3 (list) Main Condition1 (list)

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ɹ Header Footer Navigation Bars (13 menus) Margen Sub Condition1 (list) Sub Condition2 (list) Main Condition2 (list) Main Condition3 (list) Main Condition1 (list)

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ɹ Header Footer Navigation Bars (13 menus) Margen Sub Condition1 (list) Sub Condition2 (list) Main Condition2 (list) Main Condition3 (list) Main Condition1 (list) Scope works (so-called encapsulation)

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How to program

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Web Components is based on three specifications.

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Custom Elements Shadow DOM ES Modules Three specifications ※ HTML Imports

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HTML Imports ?

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⚠Attention⚠ “HTML Imports” is deprecate and will remove

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1. Custom Elements

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Custom Elements is a function for creating your own custom HTML elements. Custom Elements can have its own script action and CSS styling. This is part of web components, but you can use it alone. Custom Elements see also: https://developer.mozilla.org/ja/docs/Web/Web_Components/Custom_Elements

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custom elements, name is “-” required inheritance of HTMLElement class is required

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lifecycle methods

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constructor() connectedCallback() disconnectedCallback() attributeChangedCallback(attributeName, oldValue, newValue, namespace) adoptedCallback(oldDocument, newDocument) lifecycle callbacks

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constructor() connectedCallback() disconnectedCallback() attributeChangedCallback(attributeName, oldValue, newValue, namespace) adoptedCallback(oldDocument, newDocument) lifecycle callbacks Invoked when the custom element is created or updated.

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constructor() connectedCallback() disconnectedCallback() attributeChangedCallback(attributeName, oldValue, newValue, namespace) adoptedCallback(oldDocument, newDocument) lifecycle callbacks ※Which attributes to notice change for is specified in a static get observedAttributes method

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define the name of the attribute you want to monitor

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It must be returned as an array of strings

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using getter/setter

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Will not DOM be drawn without being styled depending on the drawing timing ?

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whenDefined method is return “Promise”

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2. Shadow DOM

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The ShadowRoot interface of the Shadow DOM API is the root node of a DOM subtree that is rendered separately from a document's main DOM tree. Shadow DOM see also: https://developer.mozilla.org/ja/docs/Web/API/ShadowRoot

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Encapsulation !!

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How to create Shadow DOM

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Element.attachShadow method creates Shadow DOM

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Unless there is a particular reason, in “open” mode

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Shadow DOM styling

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:host() :host-content() ::slotted() Shadow DOM styling

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3. ES Modules

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See this link↓↓ https://developer.mozilla.org/ja/docs/Web/ JavaScript/Reference/Statements/import Sorry…

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Browser compatibility

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image by: https://caniuse.com/#search=custom%20elements

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image by: https://caniuse.com/#search=shadow%20dom

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image by: https://caniuse.com/#search=modules

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Practical usage

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Use “lit-html” Use “Polymer” Use “webcomponents.js” Combine with other UI libraries Practical usage

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Web Components for future change, migration Standardize and coexist with other frameworks In the end