RxBLELibraries/react-native-ble

import React, { useState, useEffect } from 'react';
import {
  Text,
  View,
  PermissionsAndroid,
} from 'react-native';

import {
    BleManager,
    nativeDevice
  } from 'react-native-ble-plx';

export default function App() {

  const bleManager = new BleManager();

  useEffect(() => {
    const subscription = bleManager.onStateChange(async (state) => {
        if (state === 'PoweredOn') {
            const permission = await requestLocationPermission();
            console.log('permission: ', permission);
            if(permission){
                scanAndConnect();
                subscription.remove();
            }
        }
    }, true);
  });

  useEffect(() => {
    async function monitor() {
      const subscription = await bleManager.monitorCharacteristicForDevice("8C:AA:B5:85:F4:EE", 
        "4fafc201-1fb5-459e-8fcc-c5c9c331914b", 
        "beb5483e-36e1-4688-b7f5-ea07361b26a8", 
        (error, characteristic) => {
            if (error) { console.log('Error Message: ', error.message); return }
            console.log("characteristic: ", characteristic);
        });
      subscription.remove();
      }
    monitor();
  },[]);

  async function scanAndConnect() {
    await bleManager.startDeviceScan(null, null, (error, device) => {
      if (error) {
          console.log('ERRO: ', error);
          return
      }
      if (device.localName !== null) {
        if (device.localName.substr(0, 9) === 'SpeedTest') {
          console.log('1');
          bleManager.stopDeviceScan();
          bleManager
            .connectToDevice(device.id, {autoConnect: true})
            .then(device => { return device.discoverAllServicesAndCharacteristics() })
            .then(device => {
              readData(device);
            })
            .catch(error => {
              console.log(error);
              bleManager
                .isDeviceConnected(device.id)
                .then(res => console.log(res))
                .catch(err => console.log(err));
              console.log('error.message: ', error.message);
              device.cancelConnection();
              scanAndConnect();
            } )
        }
      }

    } ) 
  };

  async function readData(device) {
  device.services()
      .then( services => {
        const characteristics = [];
        services.forEach( ( service, i ) => {
          service.characteristics()
            .then( c => {
              characteristics.push( c );
              if ( i === services.length - 1 ) {
                console.log('characteristics: ', characteristics );
              }
            } )
          })
      })
  }

  async function requestLocationPermission() {
    const granted = await PermissionsAndroid.request(
      PermissionsAndroid.PERMISSIONS.ACCESS_FINE_LOCATION,
      { title: "Permição para Bluetooth BLE",
        message: "Este App pode acessar o Bluetooth LE. ",
        buttonNeutral: "Ask Me Later",
        buttonNegative: "Cancel",
        buttonPositive: "OK"
      });
    if (granted === PermissionsAndroid.RESULTS.GRANTED) {
      console.log("You can use the Bluetooth LE");
      return (true)
    } else {
      console.log("Bluetooth LE permission denied");
      return (false)
    }
  }

  return (
      <View>
          <Text>Let’s start</Text>
      </View>
  );
}