ClojureScript optimization and source maps support
by Michal Marczyk for Clojure
Full source maps support in ClojureScript; a web-based benchmarking app capable of comparing performance across revisions of a project, with good UX (GitHub links for all revisions / revisions causing regressions etc.); automated browser REPL tests; performance tuning of the core codebase, including a thorough review of code generated under advanced compilation to discover inefficiencies (e.g. spots where the structure of the ClojureScript code defeats Closure compiler's optimization effors).