How to use the react-native-nfc-manager.onStateChanged function in react-native-nfc-manager

console.log('launch tag', tag);
                    if (tag) {
                        this.setState({ tag });
                    }
                })
                .catch(err => {
                    console.log(err);
                })
            NfcManager.isEnabled()
                .then(enabled => {
                    this.setState({ enabled });
                })
                .catch(err => {
                    console.log(err);
                })
            NfcManager.onStateChanged(
                event => {
                    if (event.state === 'on') {
                        this.setState({enabled: true});
                    } else if (event.state === 'off') {
                        this.setState({enabled: false});
                    } else if (event.state === 'turning_on') {
                        // do whatever you want
                    } else if (event.state === 'turning_off') {
                        // do whatever you want
                    }
                }
            )
                .then(sub => {
                    this._stateChangedSubscription = sub; 
                    // remember to call this._stateChangedSubscription.remove()
                    // when you don't want to listen to this anymore