title: Mongoose TTL indexes callback in NodeJS
body: <p>I want to delete an entry form <code>user's activity</code> collection in an hour <em><strong>if nothing happened on it</strong></em>. I'm getting it with Mongoose TTL index <code>expireAfterSeconds</code>. But I also need to send push notification to the user, the activity belongs to, when that activity is deleted.</p>
  <p>Is there a way, I can get callback when expiration is performed by MongoDb TTL? Or any other way without using crons as creating multiple jobs might not be good for server (according to my pov). Also I'm updating expiry time so cron would also be difficult to pause, stop, restart, etc</p>