Import and export CommonJS modules in js_of_ocaml
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Import and export CommonJS modules in js_of_ocaml

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Working with Javascript CommonJS modules in js_of_ocaml can be difficult. commonjs_of_ocaml seeks to make things easier with a simple module and ppx syntax extension.

Installing / Getting started

You'll need opam to install this module.

opam install commonjs_of_ocaml

Alternatively, you can install from the repo itself

git clone
cd commonjs_of_ocaml
opam pin add commonjs_of_ocaml .

Include commonjs and commonjs_ppx in your -packages switch with ocamlbuild and you're on your way.

You can require commonjs compliant Javascript packages into your OCaml files as follows:

let my_module = [%require "./my_module"]

Alternatively, if you're working in a situation where you want to provide a fallback if a commonjs loader is not available, or a module is not available:

let my_module = [%require_or_default "./my_module" my_fallback_variable]

This, internally, wraps a try block around the require statement, and is useful for libraries where users may be attaching their modules directly to the DOM window where they're not using a commonjs loader.

You can also expose your OCaml library to commonjs, for easy calling from native Javascript:

let () =
  CommonJS.export my_module

When you want to test your library, simply feed the js file produced by js_of_ocaml through a tool such as Browserify and your OCaml code should be bundled with its dependencies.

An example of importing and using the PPX is included in the tests directory.


The project uses oasis for building. You'll need js_of_ocaml installed to do this.

If you need to edit this project, clone the project:

git clone
cd commonjs_of_ocaml
ocaml -configure
ocaml -build

To run the test suite:

ocaml -configure --enable-tests
ocaml -test


Packages such as Browserify work by looking for calls to require in the Javascript AST. The code js_of_ocaml produces is minified in such a way that it's difficult for tools to find dependencies it has.

By using a PPX, we can embed the raw string requiring the Javascript module.


Fork the repo and make a pull request, and I'm more than happy to take a look!


This project is MIT licensed.