fast-proj

Fast coordinate conversions for JavaScript and TypeScript. Optimized arithmetic and typed-array batching support reusable output buffers and in-place conversion, with no per-point allocations in the batch APIs, and an optional Rust/WebAssembly SIMD backend for large batches.

npm install fast-proj

package	contents	docs
fast-proj	UTM, transverse Mercator and Web Mercator ↔ WGS84, GCJ-02, GeoJSON helpers, wasm	API · from proj4 · changelog

Performance

Batch speedups for 10,000 points (median of 31 samples, mean of three runs; higher is faster). UTM zone 33N against a reused proj4 2.22 converter:

Operation	Backend	Node 24	Bun 1.4	Chromium 156
WGS84 → UTM	JavaScript	8.5×	4.2×	9.8×
	WebAssembly	13.4×	6.0×	14.9×
UTM → WGS84	JavaScript	7.3×	4.2×	8.4×
	WebAssembly	10.6×	6.0×	11.9×
UTM → GeoJSON LineString	JavaScript	6.9×	3.8×	7.3×
	WebAssembly	9.4×	5.1×	10.4×

GCJ-02 against gcoord 1.0.7:

Operation	Backend	Node 24	Bun 1.4	Chromium 156
WGS84 → GCJ-02	JavaScript	29.6×	22.6×	20.3×
	WebAssembly	39.0×	29.1×	28.2×
GCJ-02 → WGS84	JavaScript	14.8×	12.7×	13.0×
	WebAssembly	24.5×	17.1×	20.0×

UTM zone 50 with geographic: GCJ02 against proj4 + gcoord:

Operation	Backend	Node 24	Bun 1.4	Chromium 156
UTM → GCJ-02	JavaScript	16.6×	11.3×	13.0×
	WebAssembly	24.6×	17.5×	18.7×
GCJ-02 → UTM	JavaScript	13.2×	10.4×	12.1×
	WebAssembly	21.5×	14.1×	19.2×

Web Mercator (EPSG:3857) against proj4:

Operation	Backend	Node 24	Bun 1.4	Chromium 156
WGS84 → Web Mercator	JavaScript	13.0×	3.0×	11.6×
	WebAssembly	14.1×	3.0×	11.6×
Web Mercator → WGS84	JavaScript	15.6×	2.7×	14.4×
	WebAssembly	17.8×	3.7×	14.8×

Timings vary with hardware, runtime and dataset. See the full benchmark and reproduction commands.

Development

Uses Bun workspaces (package manager), vitest, oxlint, oxfmt, TypeScript 7 and Rust 1.99 (for the wasm build; rustup target add wasm32-unknown-unknown). A devcontainer is included.

bun install
bun run check    # format, lint, typecheck, build (TS + wasm), test
cd packages/fast-proj && bun run bench    # Node, Bun and Chromium
bun changeset    # describe a user-facing change for the CHANGELOG

Releases: see .changeset/README.md.

License

MIT