function windowEventsPlugin(userConfig = {}) {
  return {
    name: 'window-events',
    EVENTS: EVENTS,
    config: userConfig,
    bootstrap: ({ instance }) => {
      // Dispatch events when visitor leaves window
      mouseOut(leftWindow => {
        instance.dispatch({
          type: (leftWindow) ? EVENTS.windowLeft : EVENTS.windowEnter,
        })
      })
    }
  }
}
`windowEnter` - Fires when visitor enters the window.
This fires only when coming back into the window after leaving it.