Text speech for nearest locatoin

tts.js

/**
* this code snippet will fetch user location data in every 300 meter
* fetch nearest attractions from aws lambda
* speak - location name and addresss (most nearest one)
*/

import Expo from 'expo';
import React, { Component } from 'react';
import { Platform, Text, View, StyleSheet } from 'react-native';
import { Constants, Location, Permissions, Speech  } from 'expo';

const dataUrl = "https://XXXXXXXXXXXXXXXXXXXXXXXX.amazonaws.com/dev/get-landmarks?"; //aws lambda api
// distanceInterval: 300 which will give users location in every 300 meters
const GEOLOCATION_OPTIONS = { enableHighAccuracy: true, timeout: 20000, maximumAge: 1000, distanceInterval:300 }; 

console.disableYellowBox = true; // disable warning

export default class App extends Component {
  constructor(props){
    super(props);
    this.state = {
      location: { coords: {latitude: 0, longitude: 0}}  
    }
    this.location = null;
  }

  componentWillMount() {
    // watchPostionAsync will watch users postion and call locationChanged callback when new data comes
    Location.watchPositionAsync(GEOLOCATION_OPTIONS, this.locationChanged);
    Speech.speak("Hello Road Tripper! Hope You are having an amazing day.");
  }

  fetchLandmarks = (position) => {
    /**
    * fetch the nearest attractions using users current postion
    * fetches attraction within 500 meter
    */
    let url = dataUrl+"lat="+position.coords.latitude+"&lon="+position.coords.longitude+"&distance="+0.5
    fetch(url)
      .then((response)=>response.json())
      .then((resJson)=>{
        resJson = JSON.parse(resJson)
        Speech.stop(); //stops speech if it is running already
        if (resJson["landmark_data"] && resJson["landmark_data"].length >= 3){
            // textToRead holds the nearest 3 attractions address and name string.
            let textToRead = resJson["landmark_data"].slice(3).map((item) => item.name + "."+item.address)
            /*** this.lastLocation holds the last text from of attraction
            * if the last text doesn't match the current one then the speech
            * starts again
            */
            if (this.lastLocation !== textToRead[0]) {
              Speech.speak(textToRead[0])
              this.lastLocation = textToRead[0]
            }
        }else {
          Speech.speak("no Data found.")
        }
      })

  }
  locationChanged = (location) => {
    this.fetchLandmarks(location)
    region = {
      latitude: location.coords.latitude,
      longitude: location.coords.longitude,
      latitudeDelta: 0.1,    // zoom level
      longitudeDelta: 0.05,  // zoom level
    },
    this.setState({location, region})
  }

  render() {
    return (
        <Expo.MapView
          style={{ flex: 1 }}
          showsUserLocation={true}
          region={this.state.region}
        />
    );
  }
}