Collection.insert documentation at http://mongodb.github.io/node-mongodb-native/api-generated/collection.html#insert states it returns null ("Returns: null"). In fact, it returns the collection. The significance is the fact that code can be chained.

var mongo = require('mongodb');
var assert = require('assert');
var server = new mongo.Server('localhost', 27017,

{auto_reconnect: true}

);
var db = new mongo.Db('dbnameGoesHere', server,

{w: 1, j: true}

);

db.open(function(err, db) {
var collection = db.collection('collectionNameGoesHere');
var result = collection.insert({}, function(err, doc)

{ assert.equal(arguments.length, 2); // close event-loop db.close(); }

);
assert(result instanceof mongo.Collection);
});