Getting Started

react-native-nitro-h3 binds Uber’s H3 C library into a React Native app through Nitro Modules, so an H3 call runs in native code and answers a bigint.

1. Install the Package

Add the package together with Nitro Modules:

bun

bun add react-native-nitro-h3 react-native-nitro-modules

npm

npm install react-native-nitro-h3 react-native-nitro-modules

npx expo install react-native-nitro-h3 react-native-nitro-modules installs the same versions in an Expo project, because Expo pins no version of its own for either package and hands both to the project’s package manager.

2. Set Up the Native Projects

React Native CLI

Install the iOS pods, which links the native module into the iOS project:

cd ios && pod install

Expo

Expo Go cannot load a native module, so generate the native projects for a development build:

npx expo prebuild

3. Rebuild the App

React Native CLI

Rebuild the app so the native module is linked, with npx react-native run-ios or npx react-native run-android.

Expo

Build and start the development build with npx expo run:ios or npx expo run:android.

First Call

One coordinate and one resolution give one cell, and that cell’s ring of neighbours comes back as a typed array:

import {
  latLngToCell,
  gridDisk,
  cellToString,
} from 'react-native-nitro-h3'

// the H3 cell for San Francisco at resolution 9
const cell = latLngToCell(37.7749, -122.4194, 9) // 617700169957507071n

// the cell and its six neighbours
const neighbours = gridDisk(cell, 1) // BigUint64Array(7)

const hex = cellToString(cell) // "89283082803ffff"

latLngToCell returns a bigint, and gridDisk returns a BigUint64Array. Both are explained in Cell Indexes and bigint.

From here, Migrating from h3-js covers a move off h3-js, Typed Arrays and Batch Calls covers workloads over many cells, and the API Reference documents every exported function.