Web Components

It's all rainbows and unicorns! Is it?

Sara HARKOUSSE

UNITED DEV CONF

Minsk, 6,7 April 2017

http://vignette2.wikia.nocookie.net/weirdcommunity/images/a/a2/Rainbow-flow-abstract-backgrounds-for-powerpoint.jpg/revision/latest?cb=20130603085532

SARA HARKOUSSE

@Sara_harkousse

Tech Lead, front-end Web developer at Dassault Systèmes

3D design & PLM software

Electronics and Computer Science Engineer by training

About me

@UnitedDevConf #webcomponents

Women in Tech

Duchess France

@duchessfr

duchess-france.org

Elles bougent (Girls on The Move)

@ellesbougent

ellesbougent.com

@UnitedDevConf #webcomponents @Sara_harkousse

Web Components

It's all rainbows and unicorns! Is it?

http://vignette2.wikia.nocookie.net/weirdcommunity/images/a/a2/Rainbow-flow-abstract-backgrounds-for-powerpoint.jpg/revision/latest?cb=20130603085532

"The web components revolution"
"A Tectonic shift for web development"
"Web components are a game changer"

Web components'

public image

@UnitedDevConf #webcomponents @Sara_harkousse

Outline of this talk

@UnitedDevConf #webcomponents @Sara_harkousse

Motivation
Refresher on web components
Dive deep
Concluding remarks

Motivation

@UnitedDevConf #webcomponents @Sara_harkousse

Modular architecture

Filterable Product Table

Search Bar

Product Table

Product Row

Product Category Row

https://facebook.github.io/react/docs/thinking-in-react.html

@UnitedDevConf #webcomponents @Sara_harkousse

Angular 4.0 Component

import { Component } from '@angular/core';

@Component({
  selector: 'my-app',
  template: `<h1>Hello {{name}}</h1>`
})

export class AppComponent { name = 'Angular'; }

<my-app><h1>Hello Angular</h1></my-app>

https://embed.plnkr.co/?show=preview&show=app%2Fapp.component.ts

@UnitedDevConf #webcomponents @Sara_harkousse

Ember 2.12.0 Component

<article class="blog-post">
  <h1>{{title}}</h1>
  <p>{{yield}}</p>
  <p>Edit title: {{input type="text" value=title}}</p>
</article>

{{#each model as |post|}}
  {{#blog-post title=post.title}}
    {{post.body}}
  {{/blog-post}}
{{/each}}

https://guides.emberjs.com/v2.12.0/components/defining-a-component/

@UnitedDevConf #webcomponents @Sara_harkousse

Polymer 2.0 Element

  // Define the class for a new element called custom-element
  class CustomElement extends Polymer.Element {
    static get is() { return "custom-element"; }
    constructor() {
        super();
        this.textContent = "I'm a custom-element.";
      }
  }
  // Register the new element with the browser
  customElements.define(CustomElement.is, CustomElement);

<custom-element></custom-element>

http://plnkr.co/edit/PaCt2M?p=preview

@UnitedDevConf #webcomponents @Sara_harkousse

Frameworks make it hard to get along

@UnitedDevConf #webcomponents @Sara_harkousse

Harmony happens when there is less learning curve

@UnitedDevConf #webcomponents @Sara_harkousse

Browser support

https://www.webcomponents.org/

use webcomponents.js

Refresher on web components

@UnitedDevConf #webcomponents @Sara_harkousse

HTML Template Tag
HTML Imports
Custom Elements
Shadow DOM

HTML Template Tag

@UnitedDevConf #webcomponents @Sara_harkousse

  <template id="template">
    <div id="container">
      <img class="webcomponents" src="https://webcomponents/imgs/webcomponents-logo.svg">
    </div>
  </template>

https://jsfiddle.net/sara_harkousse/rnu8zc0c/

HTML Template Tag Usage

@UnitedDevConf #webcomponents @Sara_harkousse

var template = document.querySelector('#template');
var clone = document.importNode(template.content, true);
var host = document.querySelector('#host');
host.appendChild(clone);

https://jsfiddle.net/sara_harkousse/rnu8zc0c/

Template Tag drawbacks?

@UnitedDevConf #webcomponents @Sara_harkousse

HTML Template Tag

@UnitedDevConf #webcomponents @Sara_harkousse

A way to add inert DOM elements to your document
Not something that's going to revolutionize your apps
No two-way data binding, no binding at all

HTML Imports

@UnitedDevConf #webcomponents @Sara_harkousse

 <link rel="import" href="/imports/productRow.html">

 <script src="js/productRow.js"></script> 
 <template> 
    <!-- content-->
 <template>

How to get my component?

@UnitedDevConf #webcomponents @Sara_harkousse

var link = document.querySelector('link[rel="import"]');
var content = link.import;

// Grab DOM from productRow.html's document.
var el = content.querySelector('.productRow');
document.body.appendChild(el.cloneNode(true));

Why not this way?

@UnitedDevConf #webcomponents @Sara_harkousse

var el = require('/imports/productRow');

@UnitedDevConf #webcomponents @Sara_harkousse

<!doctype html>
<html lang="en">

    <head>
        <link rel="import" href="/imports/productRow.html">
    </head>

    <body>
        <!-- index content -->
    </body>

</html>

Render blocking

@UnitedDevConf #webcomponents @Sara_harkousse

<!doctype html>
<html lang="en">

    <head>
        <link rel="import" href="/imports/productRow.html" async>
    </head>

    <body>
        <!-- index content -->
    </body>

</html>

async unblocks the renderer

@UnitedDevConf #webcomponents @Sara_harkousse

Hammering our server

Each one of the HTML imports is another XMLHttpRequest

@UnitedDevConf #webcomponents @Sara_harkousse

Build tools for HTML Import

e.g. Vulcanizr (turns all imports into one import)

@UnitedDevConf #webcomponents @Sara_harkousse

HTML Import requires a polyfill

ES6 module?

Note: polyfill doesn’t work with file:/// protocols because it does a hidden XMLHttpRequest.

https://www.webcomponents.org/

@UnitedDevConf #webcomponents @Sara_harkousse

Shadow DOM

A tiny document
exists inside of a host element

@UnitedDevConf #webcomponents @Sara_harkousse

Key concepts

Isolated DOM
Scoped CSS
Rendering of shadow tree replaces that of host tree

@UnitedDevConf #webcomponents @Sara_harkousse

Number of shadow trees

How many shadow trees are too many?

@UnitedDevConf #webcomponents @Sara_harkousse

What's inside the Shadow DOM?

What to put in the Shadow DOM and what not to?

<my-app>

@UnitedDevConf #webcomponents @Sara_harkousse

Shadow DOM requires a polyfill

Hard to polyfill

@UnitedDevConf #webcomponents @Sara_harkousse

Use/Don't use

Shadow DOM?

callback() {
    // Use it
    this.root = this.attachShadow({mode: 'open'});

    var template = document.querySelector('#template');
    var clone = document.importNode(template.content, true);
    this.root.appendChild(clone);
}

callback() {
    // Don't Use it
    this.root = this;

    var template = document.querySelector('#template');
    var clone = document.importNode(template.content, true);
    this.root.appendChild(clone);
}

@UnitedDevConf #webcomponents @Sara_harkousse

Use/Don't use

Shadow DOM?

/* Use it */
:host {
    color: red;
}

/* Don't use it */
custom-component {
    color: red;
}

@UnitedDevConf #webcomponents @Sara_harkousse

Use AND Don't use

Shadow DOM

if (shadowflag){
    this.root = this.attachShadow({mode: 'open'});
} else {
    this.root = this;
}

custom-component, :host {
    color: red;
}

@UnitedDevConf #webcomponents @Sara_harkousse

Custom Elements

class UnitedDevConButton extends HTMLElement {...}
window.customElements.define('unitedDevCon-button', UnitedDevConButton);

<unitedDevCon-button></unitedDevCon-button>

Acts like a div

@UnitedDevConf #webcomponents @Sara_harkousse

Custom Elements

class UnitedDevConButton extends HTMLButtonElement {...}
window.customElements.define('unitedDevCon-button', UnitedDevConButton, {extends: 'button'});

<button is="unitedDevCon-button" disabled>My button!</button>

Acts like a real button

@UnitedDevConf #webcomponents @Sara_harkousse

Custom Elements Namespace

Dash (-) rule

@UnitedDevConf #webcomponents @Sara_harkousse

Custom Elements ES6 Class

class UnitedDevCon-component extends HTMLElement {
  constructor() {
    super(); // always call super() first in the ctor.
    ...
  }
  connectedCallback() {
    ...
  }
  disconnectedCallback() {
    ...
  }
  attributeChangedCallback(attrName, oldVal, newVal) {
    ...
  }

}

@UnitedDevConf #webcomponents @Sara_harkousse

Component example

Bootstrap Progress Bar

<div class="progress">
  <div class="progress-bar" style="width: 60%;">
    60%
  </div>
</div>

@UnitedDevConf #webcomponents @Sara_harkousse

Component example

class ProgressBar extends HTMLElement { 

    constructor() { 
        super(); // always call super() first in the ctor.
	this.shadow = this.attachShadow({mode: 'open'});
	this._complete = 0;				
    }

    get complete() {
        return this._complete;
    }

    set complete(val) {
        this.setAttribute('complete', val);
    }	
}

https://jsfiddle.net/sara_harkousse/kwwe75yy/

@UnitedDevConf #webcomponents @Sara_harkousse

class ProgressBar extends HTMLElement { 
	
    static get observedAttributes() {
        return ['complete'];
    }	

    attributeChangedCallback(name, oldval, newval) {
        // code
    }	
}

https://jsfiddle.net/sara_harkousse/kwwe75yy/

Component example

@UnitedDevConf #webcomponents @Sara_harkousse

class ProgressBar extends HTMLElement { 

    attributeChangedCallback(name, oldval, newval) {
        var innerBar = this.shadow.querySelector('.progress-bar-inner');
	switch(name) {
		case 'complete':
			this._complete =  parseInt(newval, 10) || 0;
			innerBar.style.width = this.complete + '%';
			innerBar.innerHTML = this.complete + '%';
	}
    }	
}

https://jsfiddle.net/sara_harkousse/kwwe75yy/

Component example

@UnitedDevConf #webcomponents @Sara_harkousse

class ProgressBar extends HTMLElement { 
    connectedCallback() {
        var template = `<style>
                        .progress-bar {
			    width: 50%;
			    ...
			}
			.progress-bar-inner {
			    height: 100%;
			    ....
			}
			</style>
			<div class="progress-bar">
				<div class="progress-bar-inner">${this.complete}%</div>
			</div>`; 
        this.shadow.innerHTML = template;
    }
}

https://jsfiddle.net/sara_harkousse/kwwe75yy/

Component example

@UnitedDevConf #webcomponents @Sara_harkousse

window.customElements.define('progress-bar', ProgressBar);

// Use
<progress-bar></progress-bar>

Component example

@UnitedDevConf #webcomponents @Sara_harkousse

Components on a page

<!doctype html>
<html lang="en">

    <head>
        <link rel="import" href="/imports/productRow.html">
    </head>

    <body>
        <custom-navbar style="compact"></custom-navbar>
        <custom-toolbar style="full"></custom-toolbar>
        <custom-pagecontent>
            <custom-item attr="val"></custom-item>
            <custom-input attr="val"></custom-input>
            <progress-bar></progress-bar>
        </custom-pagecontent>

        <script>
            document.querySelector('progress-bar').addEventListener(
                'customevent', function () {
                    // do something
                 }
            });
        </script>
    </body>

</html>

@UnitedDevConf #webcomponents @Sara_harkousse

General concerns

Should you load the polyfills in every bowser?

No.

@UnitedDevConf #webcomponents @Sara_harkousse

var = webComponentsSupported = ('customElements' in window
        && !!HTMLElement.prototype.attachShadow
        && 'import' in document.createElement('link')
        &&  'content' in document.createElement('template'));


function loadScript(src) {
 return new Promise(function(resolve, reject) {
   const script = document.createElement('script');
   script.src = src;
   script.onload = resolve;
   script.onerror = reject;
   document.head.appendChild(script);
 });
}

// Lazy load the polyfill if necessary.
if (!supportsCustomElementsV1) {
  loadScript('webcomponents-lite.min.js').then(e => {
    // Polyfill loaded.
  });
} else {
  // Native support. Good to go.
}

@UnitedDevConf #webcomponents @Sara_harkousse

Complex documentation

not fun documents to read

@UnitedDevConf #webcomponents @Sara_harkousse

Takeaway

You will understand some of the design decisions of major frameworks if you learn about custom elements

@UnitedDevConf #webcomponents @Sara_harkousse

Takeaway

Who is using web components?

@UnitedDevConf #webcomponents @Sara_harkousse

Web Components

It's all rainbows and unicorns! Is it?

SARA HARKOUSSE

About me

Women in Tech

Web Components

It's all rainbows and unicorns! Is it?

Web components'

public image

Outline of this talk

Motivation

Refresher on web components

Dive deep

Concluding remarks

Motivation

Modular architecture

Angular 4.0 Component

Ember 2.12.0 Component

Polymer 2.0 Element

Frameworks make it hard to get along

Harmony happens when there is less learning curve

Browser support

use webcomponents.js

Refresher on web components

HTML Template Tag

HTML Imports

Custom Elements

Shadow DOM

HTML Template Tag

HTML Template Tag Usage

Template Tag drawbacks?

HTML Template Tag

A way to add inert DOM elements to your document

Not something that's going to revolutionize your apps

No two-way data binding, no binding at all

HTML Imports

How to get my component?

Why not this way?

Render blocking

async unblocks the renderer

Hammering our server

Each one of the HTML imports is another XMLHttpRequest

Build tools for HTML Import

e.g. Vulcanizr (turns all imports into one import)

HTML Import requires a polyfill

ES6 module?

Shadow DOM

A tiny document

exists inside of a host element

Key concepts

Isolated DOM

Scoped CSS

Rendering of shadow tree replaces that of host tree

Number of shadow trees

How many shadow trees are too many?

What's inside the Shadow DOM?

What to put in the Shadow DOM and what not to?

Shadow DOM requires a polyfill

Hard to polyfill

Use/Don't use

Shadow DOM?

Use/Don't use

Shadow DOM?

Use AND Don't use

Shadow DOM

Custom Elements

Acts like a div

Custom Elements

Acts like a real button

Custom Elements Namespace

Dash (-) rule

Custom Elements ES6 Class

Component example

Bootstrap Progress Bar

Component example

Component example

Component example

Component example

Component example

Components on a page