Version française
Home     About     Download     Resources     Contact us    

This site is updated infrequently. For up-to-date information, please visit the new OCaml website at

Browse thread
[ANN] Js_of_ocaml version 1.0
[ Home ] [ Index: by date | by threads ]
[ Search: ]

[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: 2010-12-13 (13:07)
From: Jerome Vouillon <Jerome.Vouillon@p...>
Subject: [ANN] Js_of_ocaml version 1.0

I'm happy to announce the first official release of Js_of_ocaml,
a compiler from OCaml bytecode to Javascript.

This tool let you write OCaml programs that run on Web browsers.

Js_of_ocaml is easy to install, and use thereafter, as it works with
an existing installation of OCaml, with no need to recompile any
library.  It comes with bindings for a large part of the browser APIs.

The project page is:


The compiler has been used to implement some noteworthy examples,
such as:
- an interactive 3D view of the Earth
- a graph viewer


According to our benchmarks, with state of the art Javascript engines,
the generated programs runs typically faster than with the OCaml
bytecode interpreter ( ).

Js_of_ocaml performs dead code elimination in order to generate
compact code: the Javascript file produced is usually smaller than
the input bytecode file, and often much smaller.


Project home page
Get source code    darcs get


Js_of_ocaml performs a fairly faithful translation.  The order of
evaluation is preserved.  Modular arithmetic is used for integers (but
with 32 bit integer).  It does not support tail calls (function calls
in tail position), as this would be too expansive.  However tail
recursion (self call in tail position) is properly optimized.

Explicit coercion functions can be used to convert Ocaml values to
Javascript values, and conversely (for instance, to map OCaml mutable
strings to Javascript immutable UTF-16 strings, or to map OCaml
booleans to Javascript booleans).  A Camlp4 syntax extension makes it
possible to invoke Javascript methods in a type safe way.


Ocamljs is a compiler from OCaml source code to Javascript.  Jake
Donham has written a fair comparison of the two tools:

Ocamljs is a back-end to the existing OCaml compiler.  Thus, contrary
to Js_of_ocaml, you need to perform a distinct installation of OCaml
to use Ocamljs, and you have to recompile all the libraries you may

Ocamljs follows a different philosophy: it attempts to merge OCaml
datatypes with the corresponding Javascript datatypes.  For instance,
OCaml objects are implemented as Javascript objects.  Conversely,
Javascript objects are given an OCaml object type.  A mixed
representation of strings is used: mutable OCaml-style strings and
immutable Javascript strings both have the same type.  All this is
good for interoperability, but can be a source of incompatibilities
and can result in runtime errors not caught by the type checker.

Ocamljs optimizes tail recursion, but this comes at a large
performance cost.

Jerome Vouillon