app/assets/javascripts/application.admin.js
import './polifill'
import './ajax'
import './ext'
// http://stackoverflow.com/a/30652110/873870
function requireAll (r) { r.keys().forEach(r) }
import { mountComponents } from 'react-rails-ujs'
import Dashboard from 'Dashboard'
document.addEventListener('DOMContentLoaded', () => {
mountComponents({ Dashboard })
}, { passive: true })