At its core, one of the most powerful features of Node is that it is event-driven. This means that almost all the code you write in Node is going to be written in a way that is either responding to an event or is itself firing an event (which in turn will fire other code listening for that event).

Let's take a look at the code that we'll write in a later chapter that handles connecting to a MongoDB server using Mongoose, a popular Node.js MongoDB Object Document Mapper (ODM) module:

mongoose.connect(');
mongoose.connection.on('open', function() {
console.log("Connected to Mongoose...");
});

First, we tell our mongoose object to connect to the server provided as a string parameter to the function. Connecting will take an undetermined amount of time though, and we have no way of knowing how long. So, what we do is bind a listener to the open event on the mongoose.connection...