I will certainly pick this feature up when PROJ 9.8.0 is released.
If there is a build that can have this feature, without sacrificing the
usability, I will certainly include it in the default build. If not, I
will provide a second alternative build that is somewhat awkward to use.
My goal is to make an npm module that can be included as a normal
dependency with the developer not needing to do anything special because
of the WASM:
npm install ...
then
import ... from ...
Then use the imported functions as these were normal JS code. No heap8,
no malloc, no free, no special bundling, no ad-hoc build Bash scripts.
Because when the production web developer and his project manager see
this, they simply pass onto the next alternative.
This is why WASM has been so slow to take off - because at every step
there are rough edges and requirements such as this one.
This is what is currently missing from the WASM scene. The last mile.
This is why there is so little WASM in production-grade projects. WASM
has been around for more than 10 years now, and for those 10 years it
has remained mostly a flashy technological demonstrator at web
conferences - while there is a great potential in it.
On 04/01/2026 19:32, Will Cohen wrote:
Very cool!
I’m still tidying it up but I think I’ll have an (asynchronous)
solution using workers that uses those emscripten fetch calls, that
doesn’t need COOP/COEP, for
https://github.com/willcohen/clj-proj. I’m still doing a touch of
debugging but hope to cut a new release in the next week. Assuming it
works, you should feel free to reimplement!
Will
On Sun, Jan 4, 2026 at 1:27 PM Momtchil Momtchev via PROJ
<[email protected]> wrote:
There is indeed no solution for curl in WASM, so the network must
be reimplemented. This is what I meant when I said that there were
people working on this and that I was going to integrate their work.
However, currently, enabling pthread support in emscripten results
in a WASM binary that must have COOP/COEP enabled to work and this
restriction will be passed on to any user website that uses PROJ.
Many low-end hosting providers do not support this. For example,
Github Pages does not allow it.
There is a trick with a service worker that allows to manually
override the flag, but this also adds a very impractical layer to
every user of the library.
When PROJ 9.8.0 is released, with this feature, I will certainly
integrate it in the WASM bindings, but I am still not very sure
how. I will probably have two builds, one in which the WASM can be
used as a normal JavaScript npm module without any restrictions,
and one which has the network capability, but adds a restriction
that will be passed down to every user and website that uses PROJ.
The current situation with SharedArrayBuffer is the result of the
mitigation of a very serious security flaw (side-channel timing
attacks - such as Meltdown and Spectre) and was introduced as an
immediate solution in order to block these attacks. Ever since
there have been discussions about bringing it back with some kind
of security. Should this happen, shared memory multithreading will
once again be freely available in WASM for everyone.
On 04/01/2026 17:39, Javier Jimenez Shaw wrote:
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,
<[email protected]> 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 <[email protected]>
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--
Momtchil Momtchev<[email protected]> <mailto:[email protected]>
_______________________________________________
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[email protected]
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--
Momtchil Momtchev<[email protected]>
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