Now that we have our tests written (see previous recipe), we are ready to create our module (incidentally, from here on we'll be using the should version of our unit tests as opposed to assert).
In this recipe, we'll write our module in simple functional style to demonstrate proof of concept. In the next recipe, we'll refactor our code into a more common modular format centered on reusability and extendibility.
Let's open our main index.js and link it to the lib directory via module.exports.
module.exports = require('./lib');
This allows us to place the meat of our module code neatly inside the lib directory.
We'll open up lib/index.js and begin by requiring the fs module, which will be used to read an MP3 file, and setting up a bitrates map that cross references hex-represented values to bitrate values as defined by the MPEG-1 specification.
var fs = require('fs');
//half-byte (4bit) hex values to interpreted bitrates (bps)
/...