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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