shadow

Shadow is a simple base class for creating fast, lightweight Web Components with htm.

Written in JavaScript but strictly typed with JSDoc, you don’t need any transpiler or other tools. Although deno would certainly make the development process a greater joy.

Quick Start

Serve example

deno task serve

Type check your custom element

deno check ./examples/showcase/my_element.js

Print the documented API

deno doc https://dev.zaubrik.com/shadow/mod.js

Example

import { css, html, Shadow } from "../../mod.js";

export class MyElement extends Shadow {
  colors = ["yellow", "green", "pink", "red", "blue", "orange"];
  jsonUrl = null;
  h1Content = 0;
  firstContent = null;
  secondContent = null;
  anchorAttributes = {};

  static properties = {
    h1Content: {},
    secondContent: {},
    anchorAttributes: {},
  };

  static observedAttributes = ["json-url", "first-content"];

  static styles = css`
    :host {
      display: block;
      margin: 16px;
    }
    h1 {
      color: blue;
    }
    #myButton {
      border-radius: 30px;
    }
    .text {
      margin: 50px;
      color: brown;
    }
    a {
      color: blue;
    }
    .myLi {
      width: 200px;
      background-color: pink;
    }
  `;

  render() {
    return html`<h1>${this.h1Content}</h1>
      <button id="myButton" click=${this.clickHandler}>Count</button>
      <p class="text">You can change values through...</p>
      <p class="text">${this.firstContent}</p>
      <p class="text">${this.secondContent}</p>
      <ul>
        ${
      /**@type {string[]}*/ (this.jsonData.items).map((item) =>
        html`<li @class="myLi">${item}</li>`
      )
    }
      </ul>
      <p class="text"><a ...${this.anchorAttributes}>Anchor Text</a></p>`;
  }

  updated() {
    this.dom.class["myLi"]?.forEach((li) =>
      setInterval(
        () => (li.style.background =
          this.colors[Math.floor(Math.random() * 6)]),
        500,
      )
    );
  }

  clickHandler() {
    return ++this.h1Content;
  }
}

window.customElements.define("my-element", MyElement);

Attributes and Properties

Attributes

You can freely add and set attributes with the type string | null.
Changing an attribute alone does not cause a rerendering of the custom element.
If you add an attribute to observedAttributes, Shadow assigns the observed attribute’s value to the element’s property.
- The property must be defined on the class. Otherwise the property is ignored.
- The property name is the camel-cased attribute name.

Properties

You can freely define properties on your class. But you can also specify properties which cause a rerendering of the custom element on new asignments with:

static properties = { <propertyName> : {
reflect?: boolean,
render?: boolean,
wait?: boolean,
assert?: boolean,
rpc?: string
}}

You can pass the following options:

Setting ‘reflect’ to ‘true’ configures a property so that whenever it changes, its value is reflected to its corresponding attribute. Only JSON values can be reflected to attributes. (false)
Setting ‘render’ to ‘false’ stops rerendering on property changes. (true)
Wait for an assignment before rendering with the option ‘wait’. (false)
Assert with the option ‘assert’ if the input has a truthy value. (false)
Sets the RPC method name with rpc.

Discord

Feel free to ask questions and start discussions in our discord server.

Contribution

We welcome and appreciate all contributions to shadow.