I'm getting this array of user emails from the post data. I want to find the `_id` related to each email. I tried this for loop:

```
var studentIds = [];

for (var i = studentEmails.length - 1; i >= 0; i--) {
  var email = studentEmails[i];

  User.findOne({"email": email}, (err, student) => {
    if (err) {
      console.log("ERROR" + err);
    }
    if (student) {
      var id = student._id;
      studentIds.push(id);
      console.log("STUDENT: " + student);
    }
  });

}

// Outside for loop
console.log('END');

```

However, this logs the following:

```
END
STUDENT: { _id: 5a11e667d7333203337cd9a4,
  name: 'Patrick Jacobs',
  email: 'windvaan@live.nl',
  password: '$2a$10$CiSw/VH1HCaPtW6Sjz0X4.4avVoLsAH6iyF3FhidorahwLt1WDXoC',
  __v: 0 }
STUDENT: { _id: 5a0f7dfb64b5a6000417c662,
  name: 'Carlo Jacobs',
  email: 'carlojacobs91@gmail.com',
  password: '$2a$10$fiIosS4Jo5ehuCp3TfltSOnpypPMWSMvzlb7phRWmNGBtDz5W1rCG',
  __v: 0 }

```

As you can see, the `END` is being printed first. I don't want that. I'm assuming the `for` loop is asynchronous? How can I make it synchronous?

Thx in advance!