Fulfilling the encapsulation requirement

You can export multiple constructs from a single module by adding them as properties to the exports object. Constructs that are not exported are not available outside the module because Node.js wraps its modules inside a module wrapper, which is simply a function that contains the module code:

(function(exports, require, module, __filename, __dirname) {
  // Module code
});

This fulfills the encapsulation requirement of modules; in other words, the module restricts direct access to certain properties and methods of the module. Note that this is a feature of Node.js, not CommonJS.