replaceOne vs $set

These two look interchangeable and are not. One edits the fields you name; the other throws away everything you did not name.

Given:

{
  _id: 101,
  name: "Denish",
  age: 21,
  role: "admin"
}

Using:

db.users.replaceOne(
  { _id: 101 },
  {
    name: "New Name"
  }
)

The document becomes essentially:

{
  _id: 101,
  name: "New Name"
}

You replaced the document.

Whereas:

db.users.updateOne(
  { _id: 101 },
  {
    $set: {
      name: "New Name"
    }
  }
)

keeps everything else.