One way to manage React global state with EventEmitters

activityStore.js

const EventEmitter = require('events')

class ActivityStore extends EventEmitter {
  constructor() {
    this.state = 'stopped' // Whether you need this or not...?
  }
  start() {
    this.state = 'started'
    this.emit('started', this.state)
  }
  stop() {
    this.state = 'stopped'
    this.emit('stopped', this.state)
  }
}

exports.activityStore = new ActivityStore()

components.js

{activityStore} = require('./activityStore')

class ActivityComponent1 extends React.Component {
  constructor(props) {
    super(props)
    this.state = {activity: 'stopped'}
    activityStore
      .on('started', activity => this.setState({activity}))
      .on('stopped', activity => this.setState({activity}))
  }
  render() {
    return <h1>Activity has: {this.state.activity}</h1>
  }
}

class ActivityComponent2 extends React.Component {
  constructor(props) {
    super(props)
    this.state = {activity: 'stopped'}
    activityStore
      .on('started', activity => this.setState({activity}))
      .on('stopped', activity => this.setState({activity}))
  }
  render() {
    return <h1>Activity has: {this.state.activity}</h1>
  }
}

module.exports = {ActivityComponent1, ActivityComponent2}

components.test.js

// Replace the store with a test stub (maybe the real one talks to an API or something)
require('./activityStore').activityStore = require('./activityStoreStub')

// Now your components will require your test stub
{ActivityComponent1, ActivityComponent2} = require('./components')

// Test away!

// For more complicated stubbing, see https://github.com/thlorenz/proxyquireify

Keeping in good opinion-throwing fashion, this code is totally untested.

Hopefully you get the... wait for it... gist

Well it might be untested but it works and it is the only sample I have found on the web that actually does. :-)