AppDelegate.js

export default class AppDelegate extends UIResponder { // eslint-disable-line
  applicationPerformFetchWithCompletionHandler(application, completionHandler) {
    console.log('App is running in background')

    // Check for new data
    const newData = true

    // If new data exists, initiate a local notification
    if (newData) {
      // Let the OS know that there were new data and complete the task
      completionHandler(true)
    } else {
      // Otherwise, let the OS know there is no new data and complete the task
      completionHandler(false)
    }
  }
}