const indexCollection = function(db, callback) { db.collection('documents').createIndex( { "a": 1 }, null, function(err, results) { console.log(results); callback(); } ); }; code example

Example: mongo db const insertDocuments

const insertDocuments = function(db, callback) {
  // Get the documents collection
  const collection = db.collection('documents');
  // Insert some documents
  collection.insertMany([
    {a : 1}, {a : 2}, {a : 3}
  ], function(err, result) {
    assert.equal(err, null);
    assert.equal(3, result.result.n);
    assert.equal(3, result.ops.length);
    console.log("Inserted 3 documents into the collection");
    callback(result);
  });
}