The module wrapper

Before a module's code is executed, Node.js will wrap it with a function wrapper that looks like the following:

(function(exports, require, module, __filename, __dirname) {
// Module code actually lives in here
});

By doing this, Node.js achieves a few things:

• It keeps top-level variables (defined with var, const, or let) scoped to the module rather than the global object.
• It helps to provide some global-looking variables that are actually specific to the module, such as:
  • The module and exports objects that the implementor can use to export values from the module.
  • The convenience variables __filename and __dirname, containing the module's absolute filename and directory path.