nodejslearnerfiles/2.Modules-require-npm/mathfun.js

Very Good Beginnings if you want to Learn Node.js

var maxTime = 1000;

// if input is even, double it
// if input is odd, return error.
// ( call takes random amount of time < 1 sec )

var evenDoubler = function(v, callback) {
  var waitTime = Math.floor(Math.random()*(maxTime+1));
  if(v%2) {
      setTimeout(function (){
          callback(new Error("Odd Input"),null, waitTime);
      }, waitTime);
  } else {
      setTimeout(function (){
          callback(null, v*2, waitTime);
      }, waitTime);
  }
};

// We are trying to get the evenDoubler available to other JavaScript files. or Other Parts of the application.

module.exports.evenDoubler = evenDoubler;
module.exports.foo = "bar";