A presentation at Decoupled Days 2021 by Brian Perry
Brian Perry » Sr. Technology Consultant, Decoupled Architectures @ Pantheon » Initiative Coordinator: Decoupled Menus Initiative » Rocking the Chicago ‘burbs » Lover of all things components… and Nintendo d.o: brianperry @bricomedy brianperry.dev
Components have taken over the web
We’re here to talk about Web Components
Like React and Angular, right?
Web components A set of web platform APIs, not tied to a specific framework » Custom elements » Shadow DOM » HTML Templates
I ❤ components. So I should ❤ Web Components. ! So why weren’t they part of my workflow?
Warning: not an expert
I look to: @castastrophee @salem_cobalt @btopro @illepic
Can I Use Web Components? 1 IE 11 can be supported using polyfills 1
Can Can I Use Use Web Components? 2 Find many more examples at https://wild.open-wc.org/ 2
I should build an example web component. But what could be a relevant example in November 2020?
My own personal election tracker
Using <election-tracker> » Import script as JS module. Could be: » local file » NPM dependency (@backlineint/results-tracker) » Use your custom element in markup » Pass data in using attributes Note: If your component has external dependencies, you’ll need to use a bundler (Webpack, Rollup, Parcel, etc.)
Custom Elements 3 3 https://codepen.io/brianperry/pen/RwGPLBx
Shadow DOM » Encapsulated DOM Tree » Separate from main DOM » Elements won’t collide » Scoped styles » Super spooky
Building <election-tracker> Take 1: Vanilla JS
Rendering a Headline index.html <html> <head> <title>Results Tracker Heading</title> <meta charset=”UTF-8” /> </head> <body> <results-tracker headline=”Race Between Old Men Too Close To Call” /> <script type=”module” src=”src/results-tracker.js”></script> </body> </html>
results-tracker.js class ResultsTracker extends HTMLElement { constructor() { // Always call super first in constructor super(); // Create a shadow root const shadow = this.attachShadow({ mode: “open” }); // sets and returns ‘this.shadowRoot’ // Create wrapping element const wrapper = document.createElement(“div”); wrapper.setAttribute(“class”, “results-tracker”); this.headlineElement = document.createElement(“h2”); this.headlineElement.setAttribute(“class”, “results-tracker__headline”); this.headlineElement.textContent = this.getAttribute(“headline”); wrapper.appendChild(this.headlineElement); // Attach the results tracker to the shadow DOM. shadow.appendChild(wrapper); } } // Define the new element customElements.define(“results-tracker”, ResultsTracker);
Refactoring to use <template> class ResultsTracker extends HTMLElement { constructor() { super(); this.shadow = this.attachShadow({ mode: “open” }); // Templates are not referenced in the DOM, but can be referenced / cloned using js const template = document.createElement(“template”); template.innerHTML = <div class="results-tracker"> <div class="results-tracker__headline"> <h2>${this.getAttribute("headline")}</h2> </div> </div>; // Attach the template to the Shadow DOM this.shadow.appendChild(template.content); } } customElements.define(“results-tracker”, ResultsTracker);
Add scoped styling class ResultsTracker extends HTMLElement { constructor() { super(); /* Removed for brevity… / // Create CSS to apply to the shadow dom const style = document.createElement(“style”); style.textContent = :host { font-family: 'Libre Franklin', helvetica, arial, sans-serif; } h2 { margin: .5rem 0; font-family: 'Domine', serif; font-weight: 700; font-size: 36px; text-align: center; }; // Attach the styles to the shadow dom shadow.appendChild(style); / Removed for brevity… */ } }
Observe attributes and re-render if changed class ResultsTracker extends HTMLElement { // Specify observed attributes for attributeChangedCallback static get observedAttributes() { return [“headline”]; } constructor() { /* Removed for brevity */ } // Custom element lifecycle callback function attributeChangedCallback(name, oldValue, newValue) { // Compare old to new to prevent unnecessary re-rendering if (oldValue !== newValue && name === “headline”) { this.shadow.querySelector(“.results-tracker__headline h2”).textContent = newValue; } } } // Define the new element customElements.define(“results-tracker”, ResultsTracker);
That was too much work for a headline… 4 Shouldn’t this be easier? 4 https://codesandbox.io/s/results-tracker-heading-vanilla-js-lunes
Wait for it…
So. Many. Libraries.
» Lit » Stencil » FastElement » Haunted » Hybrids » Many more… Aren’t we just back where we started?
Only one way to find out… ! Building <election-tracker> Take 2: Lit
Rendering a headline (Lit version) index.html <html> <head> <title>Results Tracker Heading - Lit</title> <meta charset=”UTF-8” /> </head> <body> <results-tracker headline=”Race Between Old Men Too Close To Call” /> <script type=”module” src=”src/results-tracker.js”></script> </body> </html> (same as vanilla js version)
results-tracker.js import { LitElement, html } from “lit”; export class ResultsTracker extends LitElement { static get properties() { return { headline: { type: String }, }; } render() { return html<div class="results-tracker"> <div class="results-tracker__headline"> <h2>${this.headline}</h2> </div> </div>; } } window.customElements.define(“results-tracker”, ResultsTracker);
A lot with less » Renders custom element » Templating » Observes updates to attributes Just need to add scoped styles.
Add scoped styling import { LitElement, html, css } from “lit”; export class ResultsTracker extends LitElement { static get styles() { return css:host { font-family: "Libre Franklin", helvetica, arial, sans-serif; } .results-tracker__headline h2 { margin: 0.5rem 0; font-family: "Domine", serif; font-weight: 700; font-size: 36px; text-align: center; }; } // Properties… // Render method… } window.customElements.define(“results-tracker”, ResultsTracker);
Converting attributes // Vanilla JS - have to manually transform string attributes processCandidates() { this.candidates = JSON.parse(this.getAttribute(‘candidates’)); // … } // Define the type of your property, and LitElement will automatically // handle conversion for you. static get properties() { return { /** * An array of objects containing data for each candidate */ candidates: {type: Array}, }; } (And many other DX niceties)
Feels like a more appropriate amount of work for a headline… and especially the full results-tracker 5 https://codesandbox.io/s/election-results-tracker-thk26 5
Stencil “Compiler that generates web components” Provides extra capabilities on top of Web Components: » Prerendering » Objects-as-properties » Virtual DOM » JSX » Async Rendering
Vue Supports web components as a build target. But… It still requires the Vue library as a global dependency. !
Odds N’ Ends
Scoped Styles 6 6 https://codesandbox.io/s/election-results-tracker-global-styling-options-w0i3e?file=/src/styles.css
Here’s how I’ve been making sense of this… » Only inherited properties pierce the shadow DOM » Everything else requires the component to expose a styling hook: » CSS custom properties (variables) » Classes » Shadow Parts » Slots
Using web components with a framework custom-elementseverywhere.com outlines support for many frameworks. Support is pretty solid across the board. React has some notable limitations. !
React + Custom Elements 7 https://codesandbox.io/s/web-components-with-react-tvnwd 7
@lit-labs/react 8 https://codesandbox.io/s/lit-react-358ez 8
My (slightly) more educated views on web components » This was pretty hard to learn! » I’d turn to this for special purpose components today. » Close to getting comfortable enough to use this for a full app/design system. » I would use a library, but one close to the vanilla API.
On an infinite timescale… » I think some version of this concept will win out. » But how infinite is that timescale? » And will it be this take on web components? » Things are looking better every day…
Generic Drupal Web Components (GDWC)
Thanks! brian.perry@pantheon.io d.o: brianperry @bricomedy brianperry.dev
Component based approaches to front end development have taken over the web. From conceptual approaches like Atomic Design, to component based frameworks like React and Vue, this perspective on web development is unlikely to fall out of favor any time soon. And like many others, I love it.
There is however, one component related technology that has eluded me: web components. Web components are of a set of web APIs and standards that can be used to create custom and reusable HTML elements. A custom element that isn’t tied to a specific framework and is supported across all modern browsers truly sounds like component utopia. Yet somehow, native web components still haven’t become a major part of my front end toolset. With web component adoption increasing, it seemed like time to better understand why.
This session recounts the highs, lows, and surprises of my experience as a newcomer to web components, including:
The following code examples from the presentation can be tried out live.
The following resources were mentioned during the presentation or are useful additional information.
for free. You
can too.