Compilation Targets: WebAssembly

OCaml can compile to WebAssembly (WASM), enabling you to run high-performance OCaml code in web browsers, on the server, and in embedded environments with near-native speed.

What is WebAssembly?

WebAssembly is a binary instruction format designed as a portable compilation target for programming languages. It provides:

• Near-native performance in web browsers and standalone runtimes
• Sandboxed execution environment for security
• Broad platform support across browsers, servers, and edge computing
• Compact binary format for fast loading and parsing

Available Tools

wasm_of_ocaml

wasm_of_ocaml compiles OCaml bytecode to WebAssembly. It provides:

• Full OCaml language support, including the standard library and OCaml 5 effects
• Compatibility with existing OCaml libraries
• Integration with JavaScript through Js_of_ocaml-style bindings
• Ability to run OCaml code in browsers and WASM runtimes
• Shared infrastructure with Js_of_ocaml for web development
• 31-bit integers (similar to traditional OCaml bytecode on 32-bit systems)

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

wasm_of_ocaml is ideal when you want to leverage existing OCaml code with WebAssembly's performance characteristics while maintaining compatibility with the OCaml ecosystem.

Visit the wasm_of_ocaml documentation in the Js_of_ocaml repository to learn how to install and set up wasm_of_ocaml, compile OCaml programs to WebAssembly, interact with JavaScript APIs from WASM, and deploy WASM modules in web applications.

Wasocaml (Experimental)

Wasocaml is an experimental OCaml compiler developed by OCamlPro that targets WebAssembly GC (WASM-GC). As a research project exploring direct compilation to WASM-GC, it provides:

• Direct compilation from OCaml's Flambda intermediate representation to WASM-GC
• Native WebAssembly garbage collection support
• Optimised performance through the Flambda optimiser
• Support for functional programming language features in WebAssembly
• 31-bit integers (similar to traditional OCaml bytecode on 32-bit systems)

Important limitations: Wasocaml is based on OCaml 4.14 and does not currently support OCaml 5 effects or multicore features. As an experimental project, it should be considered for research and experimentation rather than for use in production.

Visit the Wasocaml repository to learn how to install the Wasocaml compiler switch and explore its experimental features.

Choosing a Tool

Use wasm_of_ocaml for most WebAssembly projects. It provides a mature toolchain for running existing OCaml bytecode in WebAssembly environments, with compatibility with Js_of_ocaml web bindings and OCaml 5 support.

Explore Wasocaml if you're interested in experimental approaches to WebAssembly compilation or researching direct compilation to WASM-GC, keeping in mind its current limitations and experimental status.

Learn More

• Dune Manual: Executable Linking Modes - How to specify native, bytecode, WebAssembly, or other compilation modes in Dune
• ocaml-wasm Organisation - Coordination hub for OCaml WebAssembly efforts
• WebAssembly.org - WebAssembly specification and documentation
• WASM-GC Proposal - Garbage Collection proposal for WebAssembly

Community

• Discuss OCaml Forums - Ask questions in the Ecosystem category
• ocaml-wasm Updates - Follow WebAssembly developments in OCaml