Compilation Targets: JavaScript

OCaml can compile to JavaScript, enabling you to write type-safe, high-performance code that runs in web browsers and Node.js environments.

Available Tools

Js_of_ocaml

Js_of_ocaml compiles OCaml bytecode to JavaScript. It provides:

• Excellent performance with compact output
• Strong integration with existing JavaScript libraries
• Access to browser APIs and DOM manipulation
• Support for the full OCaml language, including OCaml 5 effects
• Compatibility with most OCaml libraries and the standard library
• 32-bit integers (JavaScript's bit operations are 32-bit)

Note: While Js_of_ocaml supports OCaml 5 effects, it has limited support for Domains (multicore parallelism).

Js_of_ocaml is ideal when you want to leverage existing OCaml code in web applications or need access to the complete OCaml ecosystem.

Getting started: Visit the Js_of_ocaml documentation to learn how to install and set up Js_of_ocaml, compile your first OCaml program to JavaScript, interact with JavaScript APIs and the DOM, and integrate with web applications.

Melange

Melange compiles OCaml and Reason to JavaScript with a focus on JavaScript ecosystem integration. It provides:

• Idiomatic JavaScript output designed for readability
• Deep integration with NPM packages and JavaScript tooling
• Excellent TypeScript interoperability
• Optimised bundle sizes for modern web applications
• Support for React and modern frontend frameworks

Melange is ideal when you're building JavaScript-first applications and want seamless integration with the JavaScript ecosystem.

Getting started: Visit the Melange documentation to learn how to set up a Melange project, bind to JavaScript libraries, build web applications with Melange, and integrate with existing JavaScript tooling.

Choosing a Tool

Use Js_of_ocaml when you have existing OCaml code you want to run in the browser, need the full OCaml standard library, or want to use OCaml-native libraries.

Use Melange when you're building web applications that need to integrate tightly with JavaScript libraries, want readable JavaScript output, or need excellent TypeScript compatibility.

Learn More

• Dune Manual: Executable Linking Modes - How to specify native, bytecode, or other compilation modes in Dune
• Js_of_ocaml Manual - Comprehensive guide and API reference
• Melange Playground - Try Melange in your browser
• OCaml for Web Development - Overview of web development with OCaml

Community

• Discuss OCaml Forums - Ask questions in the Ecosystem category
• Melange Discord - Melange and Reason community