Web components are a tale of four w3c specifications. They are a hot topic now. We’ve all seen big headlines, for instance, “The Web Components revolution”, “Web Components are a game changer”, “A Tectonic Shift for Web Development”, … and so many others. They are certainly exciting and promising, nevertheless, there are some factors holding them back such as performance issues and lack of browser support. Some features seems to be more hassle than they’re worth. In this talk you’ll examine web components from a pragmatic stand point. So if you want to start using web components in production, come to learn what features can you use today. Actually, despite the still short browser support, some of web components features seems to be the best choice to start with . The assessment you’ll learn is the reflection of my personal research and work on my spare time and also feedbacks from my co-workers.

1. Web Components
It's all rainbows and
unicorns! Is it?
Sara HARKOUSSE
BlendWebMix
Lyon, 26, 27 October 2017
1

2. 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
#BlendWebMix #webcomponents 2

3. Women in Tech
Duchess France
@duchessfr
duchess-france.org
Elles bougent (Girls on The Move)
@ellesbougent
ellesbougent.com
#BlendWebMix #webcomponents @Sara_harkousse 3

4. Web Components
It's all rainbows and
unicorns! Is it?
4

5. "The web components revolution"
"A Tectonic shift for web development"
"Web components are a game changer"
Web components'
public image
#BlendWebMix #webcomponents @Sara_harkousse 5

6. Web components'
public image
#BlendWebMix #webcomponents @Sara_harkousse
"The broken promise of Web Components"
6

7. Motivation
#BlendWebMix #webcomponents @Sara_harkousse
Modular architecture
Filterable
Product Table
Search Bar Product Table
Product
Row
Product
Category
Row
7

8. 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
#BlendWebMix #webcomponents @Sara_harkousse
Ember 2.16.0 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/
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
8

9. #BlendWebMix #webcomponents @Sara_harkousse
Frameworks make it
hard to get along
9

10. #BlendWebMix #webcomponents @Sara_harkousse
Harmony happens
when there is less
learning curve
10

11. Browser support
use webcomponents.js
#BlendWebMix #webcomponents @Sara_harkousse 11

12. Refresher on web
components
Web components are a set of web platform APIs
that allow you to create new custom, reusable,
encapsulated HTML tags to use in web apps.”
#BlendWebMix #webcomponents @Sara_harkousse 12

13. Refresher on web
components
#BlendWebMix #webcomponents @Sara_harkousse
HTML Template Tag
HTML Imports
Custom Elements
Shadow DOM
13

14. HTML Template Tag
#BlendWebMix #webcomponents @Sara_harkousse
<template id="template">
<div id="container">
<img class="webcomponents" src="logo.svg">
</div>
</template>
14

15. HTML Template Tag Usage
#BlendWebMix #webcomponents @Sara_harkousse
var template = document.querySelector('#template');
var clone = template.content.cloneNode(true);
var host = document.querySelector('#host');
host.appendChild(clone);
15

16. HTML Template Tag
#BlendWebMix #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
16

17. HTML Imports
#BlendWebMix #webcomponents @Sara_harkousse
<link rel="import" href="component.html">
<link rel="stylesheet" href="style.css">
<div id="container">
<img class="rotate" src="logo.svg">
</div>
<script src="script.js"></script>
17

18. How to get my
component?
#BlendWebMix #webcomponents @Sara_harkousse
var link = document.querySelector('link[rel="import"]');
var content = link.import;
// Grab DOM from component.html's document.
var el = content.querySelector('#container');
var clone = el.cloneNode(true);
var host = document.querySelector('#host');
host.appendChild(clone);
18

19. #BlendWebMix #webcomponents @Sara_harkousse
HTML Import
requires a polyfill
ES module?
19

20. #BlendWebMix #webcomponents @Sara_harkousse
ES module
// export feature
export const Component = // …
// import feature
import {Component} from '../components/cutom-component.js';
20

21. #BlendWebMix #webcomponents @Sara_harkousse
Shadow DOM
A tiny document
exists inside of a host element
21

22. #BlendWebMix #webcomponents @Sara_harkousse
Key concepts
Isolated DOM
Scoped CSS
22

23. #BlendWebMix #webcomponents @Sara_harkousse
Shadow DOM
requires a polyfill
Hard to polyfill
23

24. #BlendWebMix #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);
}
24

25. #BlendWebMix #webcomponents @Sara_harkousse
Use/Don't use
Shadow DOM?
/* Use it */
:host {
color: red;
}
/* Don't use it */
custom-component {
color: red;
}
25

26. #BlendWebMix #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;
}
26

27. #BlendWebMix #webcomponents @Sara_harkousse
Custom Elements
class CustomButton extends HTMLElement {...}
window.customElements.define('custom-button', CustomButton);
<custom-button></custom-button>
Acts like a div
27

28. #BlendWebMix #webcomponents @Sara_harkousse
Custom Elements
class CustomButton extends HTMLButtonElement {...}
window.customElements.define('custom-button', CustomButton, {extends: 'button'});
<button is="custom-button" disabled>My button!</button>
Acts like a real button
28

29. #BlendWebMix #webcomponents @Sara_harkousse
Custom Elements
Namespace
Dash (-) rule
29

30. #BlendWebMix #webcomponents @Sara_harkousse
Custom Elements
ES6 Class
class Custom-component extends HTMLElement {
constructor() {
super(); // always call super() first in the ctor.
...
}
connectedCallback() {
...
}
disconnectedCallback() {
...
}
attributeChangedCallback(attrName, oldVal, newVal) {
...
}
}
30

31. #BlendWebMix #webcomponents @Sara_harkousse
Component example
Bootstrap Progress Bar
<div class="progress">
<div class="progress-bar" style="width: 60%;">
60%
</div>
</div>
31

32. window.customElements.define('progress-bar', ProgressBar);
// Use
<progress-bar></progress-bar>
Component example
https://jsfiddle.net/sara_harkousse/kwwe75yy/
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);
}
static get observedAttributes() {
return ['complete'];
}
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 + '%';
}
}
connectedCallback() {
var template = `<div class="progress-bar">
<div class="progress-bar-inner">${this.complete}%</div>
</div>`;
this.shadow.innerHTML = template;
}
}
#BlendWebMix #webcomponents @Sara_harkousse 32

33. #BlendWebMix #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-input attr="val"></custom-input>
<progress-bar></progress-bar>
</custom-pagecontent>
<script>
document.querySelector('custom-input').dispatchEvent(new CustomEvent('customevent', {
detail: { prop: true }
}));
document.querySelector('progress-bar').addEventListener(
'customevent', function () {
// do something
}
});
</script>
</body>
</html>
33

34. #BlendWebMix #webcomponents @Sara_harkousse
Takeaway
Template tag? yeah! why not?
Use ES module instead of HTML Imports
Use Shadom DOM with a flag
Custom Elements?? Go, Go, Go
34

35. #BlendWebMix #webcomponents @Sara_harkousse
Takeaway
You will understand some of the design decisions of
major frameworks if you learn about custom
elements
35

36. #BlendWebMix #webcomponents
Thanks for listening!
Follow for slides
@Sara_harkousse
https://github.com/SaraHarkousse
36