I'm Jagvinder Singh Reehal

• Contractor living in Cambridge
• Clients include Arm, Compare The Market, Cambridge Assessment, Ford, Reed Elsevier and Cambridge University Press
• Web developer since I graduated in 2000
• Used loads of libraries and frameworks
• Currently tech lead on a project using Vue and GraphQL

Two of the biggest changes in web development

• State
• Components

  For me React was the first library that made this possible

A component should be...

• small
• reusable
• testable
• documented
• of high quality (accessibility etc.)
• good at JUST one thing
• styleable

A component should also...

• have few or no dependencies?
• look and behave the same across browsers?
• work regardless of what else is on the page?
• be lazy loadable?
• be as easy to use as an HTML element?
• be able to be used by non-techies 🤓 without JS knowledge?

Let's build a component

• We're a React shop
• Our component uses hooks... but not all of our apps support hooks
• Do other applications within the organisation use the same library/framework?
• What if your organisation acquires another organisation?
• If your organisation publishes components do you maintain and try to keep feature parity with all versions?

What about a web component?

• Custom elements

  // create
  class TodoItem extends HTMLElement {}
  
  // register
  customElements.define("todo-item", TodoItem);
  
  // use
  <todo-item></todo-item>

• HTML templates
• Shadow DOM
• HTML imports

What is the Shadow Dom?

• Provides 'iframe like' encapsulation (for CSS) hiding implementation details ... like a native element!
• Better than an iframe e.g. accessibility, styling, etc.
• Perfect for design systems!
• Great for sharing - Twitter "sharethis tweet"
• BBC 'How I learnt to Stop Worrying and Love the Shadow Dom'

Styling Components

• Styling components can be done using
  • Regular CSS
  • CSS modules
  • CSS-in-JS
  • Shadow DOM
• Let's see how they cope with class style 💣
  and element style 👻

React Component using CSS

React component using CSS-in-JS

                    
const View = styled.div`
  color: #4d4d4d;
`;

// used like this

<View>
...
</View>
                    
                  

                    
.htZyQy {
  color: #4d4d4d;
}                      


...



                    
                  

Shadow Dom (NOT EFFECTED)

Themed Shadow Dom

            
:host{
  background-color: #FFF:
}                
:host(.dark) {
  background-color: #000:
}             
            
          

CSS Variables Shadow Dom

            
:root {
  --todo-item-background-color: orange;
  --todo-item-color: blue;
  --todo-destroy-color: black;
}         
            
          

Use your own (styled) content using a slot

            

<todo-item>
  <slot/>  
</todo-item>
            
          

Shadow DOM pitfalls

• Don't work well in forms... yet
• Polyfills (more on this later)
• 'all: initial' vs inherited properties
• Closed mode is evil

Web component troubles

• Spec change (v0 to v1) is still confusing
• Polymer the 'flagship' for web components was awful
• Horrible developer experience (example)
• All this at the time when other libraries and frameworks made things look simple
• Outdated - The broken promise of Web Components
• Attributes vs props confusion - Why I don't use web components by Rich Harris
• The biggest problem is...

The web platform is and always will be consistently inconsistent

However... usage is growing

6% of all pages today use web components

Support is excellent

Seamless integration with MOST libraries and frameworks...

• Custom Elements Everywhere checks how interoperable web components are
  
  

React 😞

• Read the issue about why
• use-custom-element hook

Vanilla web components are & will always be 💩

"Just in the same way we don't ship vanilla JavaScript, no one will ship vanilla web components either"

Jag Reehal

Lots of options!

• Angular, Vue and Svelte have built in support to create custom elements
• If you don't want a build step you could look at lit-element or Haunted for a hooks like experience

I ♥️ Stencil

The Era of Disappearing Frameworks

• Like Svelte, Stencil uses compilation
• Which results in a minimal runtime and computed bundling

Integrating web components

• Create web component, write tests and Storybook story
• Replace native component with web component
• Run E2E tests using Cypress.io after each step
• TL;DR - smaller build, state management still the same

Stencil Todo Input

            
import { Component, State, Event, EventEmitter, h } from '@stencil/core';

@Component({
  tag: 'todo-input'
})
export class TodoInput {
  @Event({ eventName: 'input-submit' }) inputSubmit: EventEmitter;
  @State() value: string;

  keyUp = e => {
    if (e.keyCode === 13) {
      this.inputSubmit.emit(this.value);
      this.value = '';
    }
  };

  render() {
    return (
      <input
        class="new-todo"
        value={this.value}
        type="text"
        autoFocus
        placeholder="What needs to be done?"
        onInput={(ev: any) => (this.value = ev.target.value)}
        onKeyUp={e => this.keyUp(e)}
      />
    );
  }
}
            
          

Integrating Stencil

• Script tags

• npm module (Stencil React Example)
• Read more about Framework Integration

Used like this in React

• Before

              const TodoInput = () => {
    const [textInput, onInputChange] = useState('');
    const { onSubmitTodo } = React.useContext(TodoStoreContext);
    const handleInputEnterPress = e => {
      if (e.key === 'Enter') {
        onSubmitTodo(textInput);
        onInputChange('');
      }
    };
    return (
      <>
        <input
          onKeyPress={handleInputEnterPress}
          className="new-todo"
          placeholder="What needs to be done?"
          autoFocus
          value={textInput}
          onChange={e => onInputChange(e.target.value)}
        />
      </>
    );
  };
            

• After

                  const TodoInput = () => {
    const { onSubmitTodo } = React.useContext(TodoStoreContext);
  
    const [customElementProps, ref] = useCustomElement({
      'input-submit': onSubmitTodo
    });
    return <todo-input autofocus {...customElementProps} ref={ref} />;
  };

Used like this in Vue

• Before

                 
  <input class="new-todo"
         autofocus
         autocomplete="off"
         placeholder="What needs to be done?"
         v-model="newTodo"
         @keyup.enter="addTodo" />         
              
            

• After

                  
  // tell Vue not to panic we know what we're doing                
  Vue.config.ignoredElements = ['todo-input'];                
  
  <todo-input @input-submit="addTodo"/>
  

But is it fast?

• React

  Before

  100

  After

  100
• Vue

  Before

  100

  After

  100

DX using Stencil web components

• Intellisense
• Typescript
• Storybook documentation using Stencil
• Testing has to change from unit to E2E - Write tests. Not too many. Mostly integration by Kent Dodds
• Use as any other HTML element
• Culture and resource has to support the change

Production ready?

Companies that use web components

Thanks for coming!

• Use whatever works for you
• It's about composable, collaborative UI components NOT vs.
• Grab some popcorn and watch the big frameworks and libraries fight it out
  
• Questions?