//area.js
var PI = Math.PI;
function circle (radius) { 
 return radius * radius * PI;
}
module.exports.circle = circle; 

var areaCalc = require('./area');
console.log(areaCalc.circle(5)); 

// MyFancyObservable.js
var util = require('util'); 
var EventEmitter = require('events').EventEmitter;
function MyFancyObservable() { 
 EventEmitter.call(this);
}
util.inherits(MyFancyObservable, EventEmitter); 

MyFancyObservable.prototype.hello = function (name) { 
 this.emit('hello', name);
};

var MyFancyObservable = require('MyFancyObservable'); 
var observable = new MyFancyObservable();
observable.on('hello', function (name) { 
 console.log(name);
});
observable.hello('john'); 

function MyClass (options) { 
 this.options = options;
}
function create(options) { 
 // modify the options here if you want
 return new MyClass(options);
}
module.exports.create = create; 

function userModel (options) { 
 var db;
 if (!options.db) {
  throw new Error('Options.db is required');
 }
 db = options.db;
 return {
  create: function (done) {
   db.query('INSERT ...', done);
  }
 }
}
module.exports = userModel; 

var db = require('./db');
var userModel = require('User')({ 
 db: db
});

app.use = function(fn){ 
 this.middleware.push(fn);
 return this;
};

var i = middleware.length; 
while (i--) { 
 next = middleware[i].call(this, next);
}

process.stdin.on('readable', function () { 
  var buf = process.stdin.read(3);
  console.dir(buf);
  process.stdin.read(0);
});