title: My given time in expireAfterSeconds is not working in ttl. row is deleted by its own within minute
body: <p><strong>here is my code...kindly review it.</strong>
  this automatically deletes the record without mentioning the seconds.
  i changed the createindex to ensureindex also ...but still not working   </p>
  
  <pre><code>var mongo = require('mongodb');
  
  var MongoClient = require('mongodb').MongoClient;
  var url = "mongodb://localhost:27017/testing5";
  
  
  var extend;
  var time = "3600";
  
  MongoClient.connect(url, function(err, db) {
    if (err) throw err;
      var dbase = db.db("testing5");
  var myobj = ({
    "name": "Adnan khan",
     "email": "xyz@gmail.com",
     "createdAt": new Date(),
  });
  
  
  dbase.collection("log_events").createIndex({ "createdAt": 1 }, { expireAfterSeconds: time })
  
  
    dbase.collection("log_events").insertOne(myobj, function(err, result) {
      if (err) throw err;
      resultant = result
  
      console.log("data inserted and will be deleted approximately after 20 seconds");
      db.close();
    });
    });
  </code></pre>