App.js

import React, { Component } from 'react';
import TeacherIntroductions from './components/TeacherIntroductions';
import './App.css';

class App extends Component {
  render() {
    return (
      <div className="App">
        <TeacherIntroductions /> 
      </div>
    );
  }
}

export default App;

index.js

import React from 'react';
import ReactDOM from 'react-dom';

import { Provider } from 'react-redux';
import store from './redux/store';

import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';

ReactDOM.render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById('root')
);

// If you want your app to work offline and load faster, you can change
// unregister() to register() below. Note this comes with some pitfalls.
// Learn more about service workers: http://bit.ly/CRA-PWA
serviceWorker.unregister();

redux-reducers-TeacherIntroductions.js

const initialState = {
  allIds: [1, 3, 4],
  byIds: {
    1: {
      name: 'Bob',
      location: 'New Zealand',
      videoUrl: 'https://www.youtube.com/embed/M7lc1UVf-VE'
    },
    3: {
      name: 'Jerry',
      location: 'Norway',
      videoUrl: 'https://www.youtube.com/embed/M7lc1UVf-VE'
    },
    4: {
      name: 'Xiao Rose',
      location: 'USA',
      videoUrl: 'https://www.youtube.com/embed/M7lc1UVf-VE'
    },
  }
}

export default (state = initialState, action) => {
  return state;
}

TeacherIntroductions.js

import React from 'react';
import { connect } from "react-redux";
//import TeacherIntroduction from './TeacherIntroduction';


const TeacherIntroduction = ({key, teacher}) => (
  <li className="teacher-introduction">{teacher}</li>
)


const TeacherIntroductions = (teachers) => (
  <ul className="teacher-introductions">
    {Object.entries(teachers.byIds).forEach(([id, info]) => {
      return <TeacherIntroduction key={id} teacher={info} />
    })}
  </ul>
)

const mapStateToProps = state => {
  return state.TeacherIntroductions
}

export default connect(mapStateToProps)(TeacherIntroductions)