import.js

....

import BleManager from 'react-native-ble-manager';
const bleManagerEmitter = new NativeEventEmitter(BleManagerModule);
...

componentDidMount() {
    AppState.addEventListener('change', this.handleAppStateChange);

    BleManager.start({showAlert: false});

    this.handlerDiscover = bleManagerEmitter.addListener(
      'BleManagerDiscoverPeripheral',
      this.handleDiscoverPeripheral,
    );
    this.handlerStop = bleManagerEmitter.addListener(
      'BleManagerStopScan',
      this.handleStopScan,
    );
    this.handlerDisconnect = bleManagerEmitter.addListener(
      'BleManagerDisconnectPeripheral',
      this.handleDisconnectedPeripheral,
    );
    this.handlerUpdate = bleManagerEmitter.addListener(
      'BleManagerDidUpdateValueForCharacteristic',
      this.handleUpdateValueForCharacteristic,
    );

    if (Platform.OS === 'android' && Platform.Version >= 23) {
      PermissionsAndroid.check(
        PermissionsAndroid.PERMISSIONS.ACCESS_COARSE_LOCATION,
      ).then(result => {
        if (result) {
          console.log('Permission is OK');
        } else {
          PermissionsAndroid.requestPermission(
            PermissionsAndroid.PERMISSIONS.ACCESS_COARSE_LOCATION,
          ).then(result => {
            if (result) {
              console.log('User accept');
            } else {
              console.log('User refuse');
            }
          });
        }
      });
    }
  }


handleAppStateChange(nextAppState) {
    if (
      this.state.appState.match(/inactive|background/) &&
      nextAppState === 'active'
    ) {
      console.log('App has come to the foreground!');
      BleManager.getConnectedPeripherals([]).then(peripheralsArray => {
        console.log('Connected peripherals: ' + peripheralsArray.length);
      });
    }
    this.setState({appState: nextAppState});
  }

  componentWillUnmount() {
    this.handlerDiscover.remove();
    this.handlerStop.remove();
    this.handlerDisconnect.remove();
    this.handlerUpdate.remove();
  }