JSS

JSS stands for JavaScript Style Sheets, a library for CSS-in-JS that allows styles to be authored as JavaScript objects rather than traditional CSS files. It compiles these definitions into CSS rules at runtime and injects them into the document, providing component-scoped styles and helping avoid global naming conflicts.

Key features include dynamic styling driven by JavaScript state or props, theming support, and a plugin system that can extend functionality. JSS also handles vendor prefixes, supports server-side rendering by extracting styles on the server, and generates deterministic class names to stabilize styling across renders. Styles are defined as JavaScript objects and applied to components, with support for nested selectors, media queries, and conditional rules. It can be used with React via adapters like react-jss or with plain JavaScript and other frameworks through the core engine.

Usage and ecosystem: JSS is one of several CSS-in-JS approaches, alongside others such as styled-components and emotion. It is valued for close integration with JavaScript execution and for enabling theming and dynamic styles. In various projects, JSS has served as a styling backend for UI libraries; however, preferences for performance, ergonomics, or syntax may lead teams to choose alternative solutions. The acronym JSS can refer to multiple entities in different contexts; this article focuses on the JavaScript styling library.