Web component decorator

Lightweight TypeScript decorators for web components for easier handling of attribute changes and cleaner code

Replaces the web component functions customElements.define(…), observedAttributes() and attributeChangedCallback(…) with decorators @define(…) and @attribute(…).

Advantages over other solutions:

• Includes Typescript definitions
• Extend any HTML element
• Non opinionated
• Lightweight
• Cleaner code

Installation

npm install --save-dev web-component-decorator

Example

import { attribute, CustomElement, define } from "web-component-decorator";

@define("my-button")
class MyButton extends HTMLElement implements CustomElement {
  constructor() {
    super();

    this.attachShadow({ mode: "open" });

    this.shadowRoot.innerHTML = `
          <style>
            button {
              padding: 5px;
            }
            #icon {
              vertical-align: middle;
            }
          </style>

          <button id="button">
              <img id="icon" alt="" width="16" height="16">          
              <slot></slot>
          </button>
        `;
  }

  @attribute("icon")
  setIcon(icon: string, oldIcon: string) {
    this.shadowRoot
      .getElementById("icon")
      .setAttribute("src", `icons/${icon}-24px.svg`);
  }
}

This example can be found in the demo directory in the repository.

API

Define custom element

@define(tagname [, options])

Parameters

Name	Type	Description
tagname	string	Name of the tag to use. Should include a '-' (minus)
options	object (optional)	Object with the form { extends: string }, where extends is the name of the HTML tag to extend

Replacement for customElements.define(tagname, classname, options). To be put right above the class declaration of the web component.

Observe attributes

@attribute(attributename)

Name	Type	Description
attributename	string	Name of the attribute

Replacement for observedAttributes() and attributeChangedCallback(…).

The decorated function has the following signature:

anyName(newValue: string, oldValue:string): void - Function to be called when an attributte changes, with the new and old value of the attribute.

A setter can also be decorated:

set anyName(value: string): void - Function to be called when an attributte changes, with the new value of the attribute.

Interface

CustomElement

Interface to implement to get access to the web component type definitions.

experimentalDecorators

Note In tsconfig.json, don't forget to add "experimentalDecorators": true to compilerOptions.

License

Copyright 2023 Edwin Martin and released under the MIT license.