xtag

xtag is an open-source JavaScript library designed to facilitate the creation and management of custom HTML elements in web applications. It emerged in the era before standardized Web Components were universally adopted, providing a lightweight abstraction that lets developers declare new tags and extend existing ones without a full polyfill setup.

The library centers around a simple API for defining elements and their behavior. Developers describe a custom tag’s lifecycle through callbacks, set up property and attribute bindings, and declare events that should be handled on the element. This approach allows for encapsulated, reusable UI components that resemble native elements, while remaining framework-agnostic.

Key features attributed to xtag include lifecycle hooks (such as creation and insertion into the DOM), attribute reflection and property accessors, event delegation, and support utilities for working with polyfills or partial browser support. The design emphasizes declarative definitions and a minimal surface area for integrating custom elements into existing pages.

Relation to standards and status: xtag was one of several approaches that helped popularize the concept of custom elements before the Web Components specifications were finalized. As native Custom Elements and Shadow DOM gained traction and standard APIs matured, the library’s usage declined. Today, xtag is primarily of historical interest or used in legacy projects, with modern development favoring standards-based Web Components or framework-specific component systems.