m3s — JavaScript / WASM

An ergonomic JS API over the shared m3s Rust core. The grid classes mirror the Python facade (m3s.H3, m3s.Geohash, …) in camelCase and produce identical results — JS and Python consume the same m3s-core crate.

This is a thin layer: it wraps the generated WASM functions into classes and computed getters and never reimplements grid math.

Install

npm install @nkarasiak/m3s

The package ships both a Node (CommonJS WASM) and a browser (ESM WASM) build; the right one is selected automatically through the exports map.

Use

import * as m3s from "@nkarasiak/m3s";
await m3s.ready();                                   // awaits WASM init (no-op on Node)

const cell = m3s.H3.fromPoint(-74.0060, 40.7128, 7); // (lon, lat, precision)
console.log(cell.id, cell.areaKm2);

const cells = m3s.Geohash.fromBbox([-74.02, 40.70, -73.93, 40.80], 6);
console.log(cells.length, cells.toIds());

await m3s.ready() is required on the web (it awaits WASM init) and harmless on Node, so the same line works everywhere.

Build from source

cd bindings/js
wasm-pack build --target nodejs --out-dir pkg      # Node build  (used by index.node.js)
wasm-pack build --target web    --out-dir pkg-web  # Web build   (used by index.web.js)

API at a glance

• Grids: A5 Geohash H3 MGRS S2 Quadkey Slippy CSquares GARS Maidenhead PlusCode EAQuad RHEALPix
• Grid methods: fromPoint(lon, lat, p?) · fromBbox([minLon,minLat,maxLon,maxLat], p?) · fromId(id) · fromIds([...]) · fromGeometry(geom, p?) · neighbors(cellOrId, depth=1, includeSelf=true) · children/parent (hierarchical grids only) · withPrecision(p) · getters name defaultPrecision precisionRange hierarchical. A5 also: cellAreaM2(p).
• Cell: id precision ring ringOpen areaKm2 centroid bounds toGeoJSON()
• CellCollection: iterable · length at slice toIds ids toPolygons toGeoJSON filter map unique neighbors(depth) refine(p) coarsen(p) totalAreaKm2 bounds
• Top-level: ready() precisionBounds(name?) geodesicAreaKm2(ring) Cell CellCollection Grid

Coordinate order

The wrapper boundary is GIS-native (lon, lat), matching the Python API, Shapely and GeoJSON. Cell ring/centroid/bounds are [lon, lat] too.

What's Python-only

The core supports point→cell and bbox→cells. These stay Python-only and are deliberately absent here:

• true polygon fill (fromGeometry reduces a polygon to its bounding box)
• precision strategies (find_precision, find_precision_for_area/use_case)
• GeoPandas / pandas export (to_gdf, to_dataframe), save, plot/explore
• dissolve, cross-grid conversion (to_h3, to_geohash, …)
• the h3-py verb vocabulary, GridBuilder, MultiGridComparator, PrecisionSelector