This simple function returns an ISODate from within last 24 hours. You can extend it to return dates from other date ranges:

var day = 1000 * 60 * 60 * 24;
var randomDate = function () {
  return new Date(Date.now() - (Math.floor(Math.random() * day)));
}

When executed it returns random ISODate() as expected:

> new Date()
ISODate("2017-04-09T19:36:43.417Z")
> randomDate()
ISODate("2017-04-09T06:43:24.249Z")

Another helpful function, this time to generate, for example, names of users:

var randomName = function() {
  // Base 36 uses letters and digits to represent a number:
  return (Math.random()+1).toString(36).substring(2);
}

And here it’s results:

> randomName()
rj611nxjre

Now we can use the following loop to insert pseudo-random documents into MongoDB:

for (var i = 1; i <= 1000000; ++i) {
  db.test.insert({
      name: randomName(),
      creationDate: randomDate(),
      uid: i
  });
}

On my laptop it took about 10 minutes to insert 1 million of random documents.

> for (var i = 1; i <= 1000000; ++i) {
    var randomName = (Math.random()+1).toString(36).substring(2);
    db.test.insert({name: randomName, creationDate: randomDate(), uid: i});
  }
... ... ... WriteResult({ "nInserted" : 1 })
> db.test.count()
1000000

A sample, generated MongoDB document looks like this:

{
        "_id" : ObjectId("58ea8976733313ff20cfc9e3"),
        "name" : "caed7zs2f6",
        "creationDate" : ISODate("2017-04-09T07:31:47.422Z"),
        "uid" : 1
}

Have fun! :-)

• Check out MongoDB Tutorial!