iOS-beacon-medium-article-componentDidMount.js

 // ...
  componentDidMount() {
    // Ranging: Listen for beacon changes
    this.beaconsDidRange = DeviceEventEmitter.addListener(
      'beaconsDidRange',
      (data) => {
        this.setState({
          dataSource: this.state.dataSource.cloneWithRows(data.beacons)
        });
      }
    );
  }
// ...