Shadow DOM
Shadow DOM is a web standard that enables encapsulation of HTML, CSS, and JavaScript within a web component, isolating it from the rest of the document. It allows developers to create reusable custom elements with their own scoped styles and markup, preventing style and script conflicts with the main DOM. This is part of the Web Components specification, which includes Custom Elements and HTML Templates.
Developers should learn Shadow DOM when building modular, reusable web components that need style and DOM isolation to avoid conflicts in large applications or when integrating third-party widgets. It is essential for creating custom elements in frameworks like Lit or Stencil, and for implementing design systems with encapsulated components. Use cases include building UI libraries, embedding isolated widgets, and developing micro-frontends where component independence is critical.