[PROJ] proj.js: JavaScript bindings for PROJ - both Node.js native & browser WASM

[Javier Jimenez Shaw]

Hi.

You mention that there is no solution for curl in wasm.
Since this PR https://github.com/OSGeo/PROJ/pull/4627 (in master, not
released yet) you can do network requests. You have to enable the proper
compilation flag.

The js function, as explained in the PR, has to be called in a worker
(thread). That is an emscripten limitation.

There is an example in https://jjimenezshaw.github.io/wasm-proj/example.html


I hope projinfo will be available soon as well.


On Sun, 4 Jan 2026, 17:21 Momtchil Momtchev via PROJ, <proj at lists.osgeo.org>
wrote:

> I am excited to announce the public availability of what should be a
> usable beta version of proj.js - JavaScript bindings for PROJ.
>
>
> https://github.com/mmomtchev/proj.js
>
> https://www.npmjs.com/package/proj.js
>
>
> proj.js is a dual-environment npm package that works both in the browser
> (compiled to WASM) and in Node.js (compiled as a native module for
> Linux, Windows and macOS).
>
> It exports both the new C++ API and the older C API to JavaScript in two
> separate modules.
>
> The package is bundler-friendly and leverages Node.js 16 exports to
> automatically load either the native version or the WASM version. It
> comes with prebuilt binaries for WASM, Linux x86, Windows x86, macOS x86
> and macOS arm8.
>
> Currently the only documentation are the unit tests and the TypeScript
> definitions. All methods are covered by TypeScript definitions which can
> be used as online help in IDEs that parse them. With very few
> exceptions, all JS methods match the C and C++ API 1:1.
>
> This is a new generation of C/C++ to JS project that leverages three new
> important technologies in the JavaScript world:
> * SWIG JSE which renders possible the automatic generation of high
> quality native-feel wrappers with minimal code (2000 lines of SWIG code
> for 200k lines of C/C++ code, an impressive 1:100 reduction)
> * emnapi which renders all Node-API modules compatible with WASM using
> the same API
> * hadron which renders possible the cross-platform compilation of
> complex C/C++ projects for JavaScript
>
> The whole project is entirely synchronous JavaScript on purpose - most
> of the methods are fast enough to be used on the main loop and adding
> async support - which is a simple flip-switch in SWIG - would add a very
> restrictive requirement to the WASM module -
> https://web.dev/articles/coop-coep - that is best avoided unless there
> is a good reason for it.
>
> The current version is available on npm and should be more or less
> usable. The unit testing is somewhat incomplete, but the nominal
> codepath of all SWIG typemaps have been tested at least once on each
> platform, including an ASAN build.
>
> Currently the main issue is the size of the WASM bundle which renders it
> impractical for most websites. Currently, the absolute minimum is about
> 1.2MB w/o libtiff, w/o proj.db, after compression and using only the C
> API. There are various options for optimising this size, but bear in
> mind, that proj.js will always be significantly larger than proj4js.
>
> This project, together with magickwand.js (ImageMagick for JS) - which
> is my basic tutorial, will be part of the SWIG JSE tutorials. proj.js is
> about advanced SWIG JSE techniques - the C++ API contains many modern
> C++>=11 features and expressing the C API in a garbage-collected
> language is not very straightforward. magickwand.js has a 1:400 code
> reduction ratio.
>
> You should know that I am not a very advanced PROJ user and my main
> interest is SWIG (though I am a user), but:
>
> * All stability problems, including memory leaks, will be thoroughly
> investigated, in the limits of what my current access to hardware allows
> * If there are methods that are incorrectly wrapped, I will fix them
> * I will fix bundler problems, this is something that is expected to
> work well, I currently have examples/testing set for the major bundlers
> such as webpack, vite, rollup and the now obsolete create-react-app
> * I do not plan to re-implement any of PROJ’ missing features in WASM -
> mainly the file and the network API - but if someone else does (I saw
> there are people working on it), I will integrate it
> * I do not plan to work on reducing PROJ’ own size, but I may eventually
> add emscripten split module support in order to reduce the initial bundle
>
> The current beta:
>
> * WASM must be built with emscripten 4.0.8
>
>     https://github.com/mmomtchev/hadron/issues/79
>
>     Will be fixed in the next hadron release.
>
> * Leaks memory if loaded/unloaded repeatedly in a Node.js worker_thread
>
>     https://github.com/nodejs/node/issues/45088
>
>     As the root cause is in Node-API itself, this won't be fixed in the
> near future, I am looking at alternative solutions. Currently every time
> you create a worker_thread that uses proj.js, when it quits, part of the
> memory is not freed until the main thread exits.
>
>
>
> --
> Momtchil Momtchev <momtchil at momtchev.com>
>
> _______________________________________________
> PROJ mailing list
> PROJ at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/proj
>
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