$ show lit/lit-element
LitElement 2.x is a lightweight base class for building fast, reusable Web Components using lit-html templating. It provides a reactive property system with attribute reflection, lifecycle hooks, and a declarative style API via tagged template literals. The library is published by Google and was the foundation for the Lit library (now in a monorepo). This repository contains the source code for version 2.x, which is in maintenance mode; active development has moved to the Lit monorepo. The codebase demonstrates solid engineering with TypeScript, comprehensive tests, and benchmarks, but relies on older dependencies (lit-html v1, TSLint, Web Component Tester) and includes legacy polyfill workarounds. It is not a data research project; it is a UI component library.
The LLM identified 3 files worth highlighting for reuse:
Core base class `UpdatingElement` that implements a reactive property system with attribute reflection, converters, change detection (`hasChanged`), and an async update cycle. It provides lifecycle hooks (`update`, `updated`, `firstUpdated`, `shouldUpdate`, `performUpdate`) and integrates with the web component lifecycle. This module is self-contained and could be extracted as a standalone reactive element base class for any custom element project.
Provides TypeScript decorators (`@customElement`, `@property`, `@state`, `@query`, `@queryAll`, `@queryAsync`, `@queryAssignedNodes`, `@eventOptions`) that simplify defining custom elements with reactive properties and DOM queries. Each decorator is a factory function that returns a property descriptor or class decorator. These are well-typed and could be reused in any LitElement-based project or adapted for other web component libraries.
Implements the `css` tagged template literal for defining scoped styles, returning `CSSResult` objects. Includes `unsafeCSS` for dynamic values and feature detection for `adoptedStyleSheets`. This pattern is reusable for any project needing safe, composable CSS-in-JS with constructible stylesheets.