LESSjs

Less.js is an open-source JavaScript implementation of the Less language, a CSS preprocessor that adds features not found in plain CSS. Less.js compiles Less source files with the .less extension into standard CSS, enabling variables, mixins, nesting, operations, and functions to be used in stylesheets. The compiler can run in two main contexts: in the browser (client-side) to compile Less dynamically at page load, or on the server (server-side) using Node.js as part of a build or deployment workflow. The project is distributed as a JavaScript library and is commonly installed via npm as the less package. In client-side usage, a script tag loads the less.js library and an accompanying .less file is linked; the library then renders the resulting CSS on the fly, though many projects prefer precompilation for production.

Key language features include variables, mixins (including parametric mixins), nested rules, operations (color arithmetic and dimension math), color functions, guards, and imports. It also supports references to variables defined in a higher scope and allows modular stylesheet organization through import functionality.

History and license: Less.js was created by Alexis Sellier in 2009 as the JavaScript implementation of the Less language. It has since been maintained by the Less.js community and core contributors. The project is released under the MIT license, and its development is hosted publicly on GitHub, with a focus on backward compatibility and ongoing improvements to the compiler and language.

See also: Less (the language) and CSS preprocessors.