CoffeeScript vs Opal

CoffeeScript is a language that compiles to JavaScript, so its output runs without a CoffeeScript interpreter. It can use existing JavaScript libraries, and JavaScript can use libraries written in CoffeeScript. Version 2 produces modern JavaScript syntax, including classes and arrow functions, and supports async functions and JSX. The `coffee` command runs scripts, compiles `.coffee` files to `.js`, and opens an interactive REPL; it can also generate inline or external source maps. Install it through npm, globally or as a project dependency. The core compiler can run in a browser or another JavaScript environment, while the command-line utility requires Node 6 or later. Its Node API compiles CoffeeScript strings and can return source maps or an abstract syntax tree. Babel transpilation is available when `@babel/core` is installed. The integrations section links to build tools, editors, frameworks, linters, formatters, and testing resources. JSX output always needs transpilation, and users must ensure their runtime supports the modern features they use or transpile the result. CoffeeScript is free and open source.

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.