js_of_ocaml vs JSweet

js_of_ocaml compiles OCaml bytecode programs into JavaScript for browsers and Node.js. It works with an existing OCaml installation and does not require libraries to be recompiled. Installation is available through opam, while Dune supports separate compilation in development and whole-program compilation in release builds. Whole-program compilation performs global dead-code elimination and cross-module optimization. The library provides a typed bridge between OCaml and JavaScript, including PPX syntax for properties, methods, constructors and objects. Browser bindings cover the DOM, Fetch, WebSockets, WebGL, workers and typed arrays. Optional packages add Lwt support, TyXML, JSON derivation and an OCaml toplevel in the browser. Documented targets include Node.js 18 or later, QuickJS-NG and modern ECMAScript 2020 browsers, including Chrome 80+, Firefox 74+, Safari 13.4+ and Edge 80+. Requirements include OCaml 4.13–5.5, Dune 3.20 or later and Menhir. The project is free and open source.

JSweet converts Java programs into TypeScript and JavaScript for browsers, mobile Web views, or Node.js. It uses Oracle's Java compiler alongside Microsoft's TypeScript compiler to generate type-checked JavaScript. The project describes the output as regular JavaScript that can work directly with JavaScript programs and libraries. Listed language features include Java-to-TypeScript syntax mapping, Java constructs, async/await, and ECMAScript targets from ES3 to ES6. JSweet lists support for more than 1,000 JavaScript libraries, frameworks, and plugins, packaged as Maven artifacts called candies. It provides Eclipse, Maven, and Gradle plugins, and names Angular, Cordova, Node.js, and Three.js among example integrations. Generated programs can use CommonJS, AMD, or UMD modules and run in browsers or Node.js. A debug mode supports debugging Java code in a browser. Setup instructions call for Git, Node.js, and Maven, then use Maven to generate JavaScript from a quickstart project. JSweet is open source and free, and is presented for Java developers building web and mobile HTML5 applications with JavaScript libraries and frameworks.