ConnectedAudioFeatures.js

import React, { Component } from 'react';
import { connect } from 'react-redux';
import { fetchAudioFeaturesById } from '../actions';
// stateless template for the display
import AudioFeatures from '../AudioFeatures'

const mapStateToProps = ({audioFeaturesById}, {trackId}) => ({ 
  audioFeatures: audioFeaturesById[trackId] 
});

const mapDispatchToProps = (dispatch) => ({ 
  fetchFeatures: (trackId) => dispatch(fetchAudioFeaturesById(trackId)) 
});

class ConnectedAudioFeatures extends React.Component {
  ...
  componentWillMount() {
    const { fetchFeatures, trackId } = this.props;
    fetchFeatures(trackId);
  }
  render() {
    const { audioFeature } = this.props
    return (<AudioFeatures audioFeature={audioFeature}/>)
  }
  ...
};
      
export default connect(mapDispatchToProps, dispatchToProps)(ConnectedAudioFeatures);