expo/src/Pedometer.js

// @flow

import { NativeEventEmitter, NativeModules } from 'react-native';
import invariant from 'invariant';

const PedometerEventEmitter = new NativeEventEmitter(
  NativeModules.ExponentPedometer
);

type PedometerResult = { steps: number };
type PedometerUpdateCallback = (result: PedometerResult) => void;
type PedometerListener = { remove: () => void };

let _listenerCount = 0;

export function watchStepCount(
  callback: PedometerUpdateCallback
): PedometerListener {
  if (_listenerCount === 0) {
    NativeModules.ExponentPedometer.watchStepCount();
  }
  _listenerCount++;

  const listener = PedometerEventEmitter.addListener(
    'Exponent.pedometerUpdate',
    callback
  );

  return {
    remove() {
      listener.remove();
      _listenerCount--;
      if (_listenerCount === 0) {
        NativeModules.ExponentPedometer.stopWatchingStepCount();
      }
    },
  };
}

export async function getStepCountAsync(
  start: Date,
  end: Date
): Promise<PedometerResult> {
  invariant(
    start <= end,
    'Pedometer: The start date must be smaller than the end date.'
  );
  return await NativeModules.ExponentPedometer.getStepCountAsync(
    start.getTime(),
    end.getTime()
  );
}

export async function isAvailableAsync(): Promise<boolean> {
  return await NativeModules.ExponentPedometer.isAvailableAsync();
}