ClojureScript vs Opal

ClojureScript is a compiler that turns Clojure code into JavaScript for client and embedded application development wherever JavaScript reaches. It brings Clojure data structures and constructs—including functional programming, macros, destructuring, and polymorphism—into JavaScript environments. Its output is compatible with Google Closure Compiler advanced compilation, which can minify output and eliminate dead code. REPL support enables interactive development and testing in a browser or Node.js; the quick start uses browser output by default and selects Node.js output with a target setting. ClojureScript supports both ClojureScript and JavaScript dependencies, with React demonstrated in the quick start. Listed build tools include shadow-cljs, Figwheel, Leiningen, and lein-cljsbuild. Editor resources cover Cursive, Emacs, VS Code, Light Table, Sublime Text, Vim, and Atom. Documentation includes compiler and REPL options, dependencies, advanced compilation, source maps, and JavaScript module support marked Alpha. The project is open source under the Eclipse Public License 1.0 and lists Linux, macOS, Windows, web, and self-hosted environments.

Opal is a Ruby-to-JavaScript source-to-source compiler that converts Ruby ahead of time into plain JavaScript, without a runtime interpreter. It includes implementations of Ruby core and standard libraries. Ruby code can call JavaScript, JavaScript can call Ruby, and native JavaScript classes can be treated as Ruby classes. The project describes sharing a gem, objects, and specs between server and client code.

Opal can run in browsers and JavaScript environments including Node.js, Deno, Bun, and QuickJS. For its upcoming 2.0 release, the project lists current and previous stable Firefox, Chrome, Safari, and Edge as supported, while Internet Explorer is unsupported. That release targets ES2021 and has no transpilation fallback for older JavaScript engines. Listed integrations include Rails, Sinatra, Roda, and static apps; the Rails example uses opal-rails and requires opal_ujs and turbolinks. Installation is through `gem install opal` or by adding the gem to a Gemfile. The gemspec declares Ruby >= 2.3, and CI exercises Ruby 3.0 through 4.0 and JRuby. Opal is MIT-licensed and free, with CLI and API access. Support channels include Slack, Stack Overflow’s #opalrb tag, and GitHub issues.