How to create a new db in mongoose?

If I use Mongoose in node.js I need to do:

var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/myDB');

But what if I just installed mongodb and I don't have any DB at the moment? How can I create a new DB using mongoose in node.js before doing mongoose.connect('mongodb://localhost/myDB')? Or if there is no such myDB then it will create a new one? or will throw an error that there is no such a DB?