import { Component, Prop, h } from "@stencil/core";

@Component({
  tag: "core-component",
  styleUrl: "core-component.css",
})
export class Component {
  @Prop() first: string;

  @Prop() last: string;

  render() {
    return (
      <div>
        Hello, my name is {this.first} {this.last}
      </div>
    );
  }
}

Note: the .tsx extension is required, as this is the standard for TypeScript classes that use JSX.

To use this component, just use it like any other HTML element:

<core-component first="Stencil" last="JS"></core-component>

Hosting the app

Stencil components run directly in the browser through script includes just like normal Custom Elements, and run by using the tag just like any other HTML component:

Here's an example index.html file that runs a Stencil app:

<!DOCTYPE html>
<html>
  <head>
    <title>My App</title>
    <script src="build/app.js"></script>
  </head>
  <body>
    <core-component first="Stencil" last="JS"></core-component>
  </body>
</html>

Naming Components

When creating new component tags, use the core- prefix and kebab-case.

For example: core-button, core-icon, etc. Custom Elements must contain a dashed name so they do not collide with existing html element names.

API

The API for Stencil closely mirrors the API for Custom Elements v1.

Components

Decorator	Description
`@Component()`	Indicate a class is a Stencil component.

`@Prop()`	Creates a property that will exist on the element and be data-bound to this component.
`@State()`	Creates a local state variable that will not be placed on the element.
`@Method()`	Expose specific methods to be publicly accessible.

High Level Component Example

@Component({
  tag: "core-component",
  styleUrls: {
    ios: "component.ios.css",
    md: "component.md.css",
    wp: "component.wp.css",
  },
})
export class Component {
  /**
   * 1. Own Properties
   * Always set the type if a default value has not
   * been set. If a default value is being set, then type
   * is already inferred. List the own properties in
   * alphabetical order. Note that because these properties
   * do not have the @Prop() decorator, they will not be exposed
   * publicly on the host element, but only used internally.
   */
  num: number;
  someText = "default";

  /**
   * 2. Reference to host HTML element.
   * Inlined decorator
   */
  @Element() el: HTMLElement;

  /**
   * 3. State() variables
   * Inlined decorator, alphabetical order.
   */
  @State() isValidated: boolean;
  @State() status = 0;

  /**
   * 4. Public Property API
   * Inlined decorator, alphabetical order. These are
   * different than "own properties" in that public props
   * are exposed as properties and attributes on the host element.
   * Requires JSDocs for public API documentation.
   */
  @Prop() content: string;
  @Prop() enabled: boolean;
  @Prop() menuId: string;
  @Prop() type = "overlay";

  /**
   * Prop lifecycle events SHOULD go just behind the Prop they listen to.
   * This makes sense since both statements are strongly connected.
   * - If renaming the instance variable name you must also update the name in @Watch()
   * - Code is easier to follow and maintain.
   */
  @Prop() swipeEnabled = true;

  @Watch("swipeEnabled")
  swipeEnabledChanged(newSwipeEnabled: boolean, oldSwipeEnabled: boolean) {
    this.updateState();
  }

  /**
   * 5. Events section
   * Inlined decorator, alphabetical order.
   * Requires JSDocs for public API documentation.
   */
  @Event() coreClose: EventEmitter;
  @Event() coreDrag: EventEmitter;
  @Event() coreOpen: EventEmitter;

  /**
   * 6. Component lifecycle events
   * Ordered by their natural call order, for example
   * WillLoad should go before DidLoad.
   */
  componentWillLoad() {}
  componentDidLoad() {}
  componentWillUpdate() {}
  componentDidUpdate() {}
  componentDidUnload() {}

  /**
   * 7. Listeners
   * It is ok to place them in a different location
   * if makes more sense in the context. Recommend
   * starting a listener method with "on".
   * Always use two lines.
   */
  @Listen("click", { enabled: false })
  onClick(ev: UIEvent) {
    console.log("hi!");
  }

  /**
   * 8. Public methods API
   * These methods are exposed on the host element.
   * Always use two lines.
   * Public Methods must be async.
   * Requires JSDocs for public API documentation.
   */
  @Method()
  async open(): Promise<boolean> {
    // ...
    return true;
  }

  @Method()
  async close(): Promise<void> {
    // ...
  }

  /**
   * 9. Local methods
   * Internal business logic. These methods cannot be
   * called from the host element.
   */
  prepareAnimation(): Promise<void> {
    // ...
  }

  updateState() {
    // ...
  }

  /**
   * 10. render() function
   * Always the last one in the class.
   */
  render() {
    return (
      <Host
        attribute="navigation"
        side={this.isRightSide ? "right" : "left"}
        type={this.type}
        class={{
          "core-is-animating": this.isAnimating,
        }}
      >
        <div class="menu-inner page-inner">
          <slot></slot>
        </div>
      </Host>
    );
  }
}

Browser Support

Web Components, specifically Custom Elements, are natively supported in Chrome and Safari and are coming to both Edge and Firefox. A dynamic polyfill loader is already included in order to only load the polyfills for the browsers that are missing specific features.

Chrome (and all Chromium based browsers)
Safari
Edge
Firefox
IE 11

Polyfills

Stencil includes a subset of the core-js polyfills for old browsers like IE11, fetch and conditionally downloads the Custom Elements v1 only when it's needed for modern browsers (EDGE and old versions of Firefox.)

Internet Explorer 11

Browsers that do not support native ESM (at the moment, only IE11 and older) will download a subset of core-js.

This subset is generated using the core-js-builder tool with the following configuration:

require("core-js-builder")({
  targets: "ie 11",
  modules: [
    "es",
    "web.url",
    "web.url.to-json",
    "web.url-search-params",
    "web.dom-collections.for-each",
  ],
  blacklist: [
    "es.math",
    "es.date",
    "es.symbol",
    "es.array-buffer",
    "es.data-view",
    "es.typed-array",
    "es.reflect",
    "es.promise",
  ],
});

In addition, the following set of polyfills are also included:

Promise
fetch()
CSS variables: We implemented our own CSS variables polyfill that integrates into the Stenciljs runtime.

All browsers

Some modern browsers like Edge do not include native support for Web Components. In that case, we conditionally load the Custom Elements v1 polyfill.

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Package last updated on 12 May 2020

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