Babel vs Opal

Babel is a JavaScript compiler that converts modern syntax into code compatible with current and older browsers or other environments. Its transformation pipeline is built from plugins, which users can combine into presets or write themselves. Babel provides transformers for the latest JavaScript and a React preset for JSX. It can also add features through third-party polyfills such as core-js, run codemods, and remove Flow or TypeScript type annotations; it does not check types. Source maps support debugging compiled output. The command-line interface can compile files or directories, watch for changes, and generate source maps. Installation documentation covers npm, Yarn, pnpm, and Bun. A standalone build can run in browsers and other non-Node.js environments, including on scripts marked text/babel or text/jsx, but the documentation recommends ahead-of-time transpilation with a Node.js build system for production. Babel is free, MIT-licensed, community-funded, and maintained by volunteers. The project directs support questions to GitHub Discussions, Slack, Stack Overflow, or Bluesky.

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.