Rails 5 API + ActiveAdmin + create-react-app on Heroku

app.js

import React, { Component } from 'react'
import { Container, Header, Segment, Button, Icon, Dimmer, Loader, Divider } from 'semantic-ui-react'

class App extends Component {
  constructor () {
    super()
    this.state = {}
    this.getDrinks = this.getDrinks.bind(this)
    this.getDrink = this.getDrink.bind(this)
  }
  componentDidMount () {
    this.getDrinks()
  }
  fetch (endpoint) {
    return new Promise((resolve, reject) => {
      window.fetch(endpoint)
      .then(response => response.json())
      .then(json => resolve(json))
      .catch(error => reject(error))
    })
  }
  getDrinks () {
    this.fetch('api/drinks')
      .then(drinks => {
        this.setState({drinks: drinks})
        this.getDrink(drinks[0].id)
      })
  }
  getDrink (id) {
    this.fetch(`api/drinks/${id}`)
      .then(drink => this.setState({drink: drink}))
  }
  render () {
    let {drinks, drink} = this.state
    return drinks
    ? <Container text>
        <Header as='h2' icon textAlign='center'>
        <Icon name='cocktail' circular />
        <Header.Content>
          List of Ingredients
        </Header.Content>
      </Header>
      <Button.Group fluid widths={drinks.length}>
        {Object.keys(drinks).map((key) => {
          return <Button active={drink && drink.id === drinks[key].id} fluid key={key} onClick={() => this.getDrink(drinks[key].id)}>
            {drinks[key].title}
          </Button>
        })}
      </Button.Group>
      <Divider hidden />
      {drink &&
        <Container>
          <Header as='h2'>{drink.title}</Header>
          {drink.description && <p>{drink.description}</p>}
          {drink.ingredients &&
            <Segment.Group>
              {drink.ingredients.map((ingredient, i) => <Segment key={i}>{ingredient.description}</Segment>)}
            </Segment.Group>
          }
          {drink.steps && <p>{drink.steps}</p>}
        </Container>
      }
    </Container>
    : <Container text>
      <Dimmer active inverted>
        <Loader content='Loading' />
      </Dimmer>
    </Container>
  }
}

export default App