@jesscss/core

@jesscss/core

The Jess compiler engine: the AST, evaluator, and single-pass serializer that turn a parsed stylesheet into CSS.

@jesscss/core is the engine at the heart of Jess — Less.js v5, a ground-up rewrite of the Less CSS preprocessor. It defines the syntax tree that every Jess parser produces, evaluates that tree (resolving variables, expanding mixins, running functions, applying extend, and folding nesting), and renders the result to CSS.

The AST lives here rather than in the jess package so that parsers can depend on the tree without pulling in the compiler, and jess can depend on the parsers plus core — avoiding a circular dependency.

What's inside

• The AST — the node types (Rules, declarations, selectors, values, …) that make up a parsed stylesheet, shared by every language grammar.
• The evaluator — resolves the language semantics over that tree.
• The single evaluate-and-emit pass (the "spine") — serializes directly over one canonical source tree instead of repeatedly cloning and re-walking nodes. This is the rewrite's headline architectural bet, and the reason the engine is being rebuilt rather than patched.
• The plugin interface — the seam that language engines (@jesscss/plugin-less, @jesscss/plugin-scss) and compatibility layers wire into.
• Diagnostics — the error and deprecation types Jess reports through.

Who uses it

This is an internal engine package. Most people should install jess and use the jess / lessc CLIs rather than depending on @jesscss/core directly. Its JavaScript/TypeScript API is not yet stabilized and is intentionally undocumented for now.

Status

Alpha. Jess renders real .less today and is being dogfooded against the Less test suite and Bootstrap, but it is early software with known rendering gaps. Published to npm under both the latest and alpha dist-tags. Please report bugs.

Links

• Repository: https://github.com/jesscss/jess
• Documentation: https://jesscss.github.io/ (currently pre-alpha content)

License

MIT