[React Native + RxJS] Create an Observable from DeviceEventEmitter - An example to handle 'locationUpdated' event

01-createObservableFromDeviceEventEmitter.js

import React, {DeviceEventEmitter} from 'react-native';
import {Observable} from 'rx-lite'

/**
 * Creates an Observable to listen to any event of DeviceEventEmitter
 * @param type {string} Event type
 */
export default createObservableFromDeviceEventEmitter$ = type => {
  let subscription;
  return Observable.fromEventPattern(
    handler => subscription = DeviceEventEmitter.addListener(type, handler),
    handler => subscription.remove()
  )
}

02-locationDidUpdate.js

import createObservableFromDeviceEventEmitter$ from './createObservableFromDeviceEventEmitter';

/**
 * Creates an Observable to listen to `locationUpdated` event
 * dispatched by Location (react-native-location)
 */
export default locationDidUpdate$ = (delay=1000) => {

  return createObservableFromDeviceEventEmitter$('locationUpdated')
      .throttle(delay) // delay of listening to events
      .map((location) => {
        // map latitude + longitude into simple object
        return {
          latitude: location.coords.latitude,
          longitude: location.coords.longitude
        }
      });
}

03-locationCheckExample.js

import Location from 'react-native-location';
import locationDidUpdate$ from './locationDidUpdate';

// init native location 
Location.requestAlwaysAuthorization();
Location.startUpdatingLocation();

// subscribe to changes
const subscription = locationDidUpdate$(2000/* delay ms */)
  .subscribe(
    (location) => {
      // do anything with the location
      console.log('location updated', location)
    },
    (e) => console.log('onError: %s', e);
  );
  
// to unsubscribe just call 
// subscription.dispose();