A powerful custom element base class that extends Lit's LitElement with integrated theming, responsive CSS utilities, RxJS-powered directives, and DOM tooling — so you can build web components that look great and stay reactive out of the box.

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Install

npm install @design.estate/dees-element
# or
pnpm install @design.estate/dees-element

This package ships as ESM and is written in TypeScript. Make sure your project targets ES2022+ with a modern module resolution strategy (e.g. NodeNext).

Usage

Everything you need is exported from the main entry point:

import {
  DeesElement,
  customElement,
  property,
  state,
  html,
  css,
  cssManager,
  directives,
} from '@design.estate/dees-element';

🧱 Creating a Custom Element

Extend DeesElement and apply the @customElement decorator:

import { DeesElement, customElement, html, css, cssManager } from '@design.estate/dees-element';

@customElement('my-button')
class MyButton extends DeesElement {
  static styles = [
    cssManager.defaultStyles,
    css`
      .btn {
        padding: 8px 16px;
        border-radius: 4px;
        background: ${cssManager.bdTheme('#0060df', '#3a8fff')};
        color: ${cssManager.bdTheme('#fff', '#fff')};
        border: none;
        cursor: pointer;
      }
    `,
  ];

  render() {
    return html`<button class="btn"><slot></slot></button>`;
  }
}

That single bdTheme() call generates a CSS variable that automatically flips between the bright and dark values when the user's theme changes — no manual toggling needed.

🎨 Theme Management with `cssManager`

The singleton cssManager is the central hub for theming and responsive layout:

Method	Purpose
`cssManager.defaultStyles`	Base styles for consistent element rendering
`cssManager.bdTheme(bright, dark)`	Returns a `CSSResult` that auto-switches between bright/dark values
`cssManager.cssForDesktop(css)`	Media-query wrapper for desktop breakpoints
`cssManager.cssForNotebook(css)`	Media-query wrapper for notebook breakpoints
`cssManager.cssForTablet(css)`	Media-query wrapper for tablet breakpoints
`cssManager.cssForPhablet(css)`	Media-query wrapper for phablet breakpoints
`cssManager.cssForPhone(css)`	Media-query wrapper for phone breakpoints
`cssManager.cssGridColumns(cols, gap)`	Generates CSS grid column widths

Example — responsive + themed styles:

@customElement('my-card')
class MyCard extends DeesElement {
  static styles = [
    cssManager.defaultStyles,
    css`
      :host {
        display: block;
        padding: 16px;
        background: ${cssManager.bdTheme('#ffffff', '#1e1e1e')};
        color: ${cssManager.bdTheme('#111', '#eee')};
        border-radius: 8px;
      }
    `,
    cssManager.cssForPhone(css`
      :host { padding: 8px; }
    `),
  ];

  render() {
    return html`<slot></slot>`;
  }
}

⚡ Reactive Properties & State

Use the standard Lit decorators, re-exported for convenience:

import { DeesElement, customElement, property, state, html } from '@design.estate/dees-element';

@customElement('my-counter')
class MyCounter extends DeesElement {
  @property({ type: String })
  accessor label = 'Count';

  @state()
  accessor count = 0;

  render() {
    return html`
      <button @click=${() => this.count++}>
        ${this.label}: ${this.count}
      </button>
    `;
  }
}

Note: This library uses the TC39 standard decorators with the accessor keyword for decorated class properties.

🔄 Theme Change Callbacks

DeesElement tracks the current theme via the goBright property and exposes an optional themeChanged callback:

@customElement('theme-aware')
class ThemeAware extends DeesElement {
  protected themeChanged(goBright: boolean) {
    console.log(goBright ? 'Switched to bright' : 'Switched to dark');
  }

  render() {
    return html`<p>Current theme: ${this.goBright ? 'bright' : 'dark'}</p>`;
  }
}

🚀 Lifecycle Helpers

DeesElement adds lifecycle utilities on top of LitElement:

@customElement('my-widget')
class MyWidget extends DeesElement {
  constructor() {
    super();

    // Runs once after the element is connected to the DOM
    this.registerStartupFunction(async () => {
      console.log('Widget connected!');
    });

    // Runs when the element is disconnected — perfect for cleanup
    this.registerGarbageFunction(() => {
      console.log('Widget removed');
    });
  }

  render() {
    return html`<p>Hello World</p>`;
  }
}

Additionally, this.elementDomReady is a promise that resolves after firstUpdated, which is handy when you need to wait for the initial render:

await this.elementDomReady;
// The element's shadow DOM is now fully rendered

📡 Directives

The directives namespace includes powerful template helpers, accessible via directives.*:

`resolve` — Render a Promise

import { html, directives } from '@design.estate/dees-element';

render() {
  return html`${directives.resolve(this.fetchData())}`;
}

`resolveExec` — Resolve a lazy async function

render() {
  return html`${directives.resolveExec(() => this.loadContent())}`;
}

`subscribe` — Render an RxJS Observable

import { html, directives } from '@design.estate/dees-element';

render() {
  return html`<span>${directives.subscribe(this.count$)}</span>`;
}

`subscribeWithTemplate` — Observable + template transform

render() {
  return html`
    ${directives.subscribeWithTemplate(
      this.items$,
      (items) => html`<ul>${items.map(i => html`<li>${i}</li>`)}</ul>`
    )}
  `;
}

Re-exported Lit directives

The directives namespace also re-exports these commonly used Lit directives:

until — render a placeholder while a promise resolves
asyncAppend — append values from an async iterable
keyed — force re-creation of a template when a key changes
repeat — efficiently render lists with identity tracking

📦 Full Export Reference

Export	Description
`DeesElement`	Base class for custom elements
`CssManager`	CSS/theme management class
`cssManager`	Singleton `CssManager` instance
`customElement`	Class decorator to register elements
`property`	Reactive property decorator
`state`	Internal state decorator
`query`, `queryAll`, `queryAsync`	Shadow DOM query decorators
`html`	Lit html template tag
`css`	Lit css template tag
`unsafeCSS`	Create `CSSResult` from a string
`unsafeHTML`	Render raw HTML in templates
`render`	Lit render function
`static` / `unsafeStatic`	Static html template helpers
`domtools`	DOM tooling utilities
`directives`	All directives (resolve, subscribe, etc.)
`rxjs` (type)	RxJS type re-export

License and Legal Information

This repository contains open-source code licensed under the MIT License. A copy of the license can be found in the LICENSE file.

Please note: The MIT License does not grant permission to use the trade names, trademarks, service marks, or product names of the project, except as required for reasonable and customary use in describing the origin of the work and reproducing the content of the NOTICE file.

Trademarks

This project is owned and maintained by Task Venture Capital GmbH. The names and logos associated with Task Venture Capital GmbH and any related products or services are trademarks of Task Venture Capital GmbH or third parties, and are not included within the scope of the MIT license granted herein.

Use of these trademarks must comply with Task Venture Capital GmbH's Trademark Guidelines or the guidelines of the respective third-party owners, and any usage must be approved in writing. Third-party trademarks used herein are the property of their respective owners and used only in a descriptive manner, e.g. for an implementation of an API or similar.

readme.md

@design.estate/dees-element