ClojureScript is a compiler and toolchain that translates Clojure (a Lisp dialect) into JavaScript, targeting the Google Closure Compiler for advanced optimization. In production, it takes ClojureScript source files, analyzes them (macro expansion, type inference, namespace resolution), emits JavaScript, and optionally invokes the Closure Compiler for bundling, minification, and dead-code elimination. The system also provides a REPL (browser and Node.js), a self-hosted compiler (ClojureScript compiling ClojureScript), a full standard library (cljs.core, clojure.string, clojure.set, etc.), a testing framework (cljs.test), a specification system (cljs.spec.alpha), source-map support, and dependency management for npm/foreign JavaScript libraries. The architecture is a library/toolchain rather than a deployed service: it runs on the JVM via Clojure and can also self-host on JavaScript runtimes. Key entry points include the CLI (cljs.main), the build API (cljs.closure/build), the compiler API (cljs.compiler.api), and the analyzer API (cljs.analyzer.api). External dependencies include Clojure, Google Closure Compiler, Google Closure Library, tools.reader, Transit, and test.check. The codebase is large and mature, with extensive regression tests and a detailed changelog, though some samples and design documents are outdated.