CoffeeScript vs Kotlin/JS

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.

Kotlin/JS is a Kotlin compiler target that converts Kotlin code, the Kotlin standard library, and compatible dependencies into JavaScript. Projects can target browsers or Node.js, including server-side and serverless applications. It supports ES5, ES2015, and ES2020 output, as well as ESM, CommonJS, UMD, and AMD modules. Projects use the Kotlin Multiplatform Gradle plugin for configuration, bundling, and JavaScript dependencies from npm. Kotlin/JS can share logic between web frontends and JVM backends, or across Android, iOS, and web clients. Kotlin wrappers are available for React and other JavaScript frameworks, including React Redux, React Router, and styled-components. Browser tests can use Karma or an experimental browser testing DSL; Node.js projects use Mocha. The documentation notes that Karma is deprecated and is not expected to receive new features or bug fixes. The Gradle plugin generates JavaScript source maps for builds. Kotlin/JS is open source and free at free, and is listed for Linux, macOS, web, and Windows.