The MongoClient connection method returns a Promise if no callback is passed to it. Below is an example using the co package to run a generator function, which is one of the most exciting innovations of ECMAScript 6.

var MongoClient = require('mongodb').MongoClient,
  co = require('co'),
  assert = require('assert');

co(function*() {
  // Connection URL
  var url = 'mongodb://localhost:27017/myproject';
  // Use connect method to connect to the Server
  var db = yield MongoClient.connect(url);
  // Close the connection
}).catch(function(err) {

The MongoClient.connect function returns a Promise that we then execute using the yield keyword of the generator function. If an error happens during the MongoClient.connect the error is caught by co and can be inspected by attaching a function to the catch method as shown above.

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