[freeCodeCamp] Start a Nodejs Server - Complete "Make it Modular"

  _/home/ubuntu/.nvm/versions/node/v4.4.5/lib/node_modules/learnyounode/exer
  cises/make_it_modular/solution/solution.js_ :  

     var filterFn = require('./solution_filter.js')
     var dir = process.argv[2]
     var filterStr = process.argv[3]  

     filterFn(dir, filterStr, function (err, list) {
       if (err)
         return console.error('There was an error:', err)  

       list.forEach(function (file) {
         console.log(file)
       })
     }) 

 _/home/ubuntu/.nvm/versions/node/v4.4.5/lib/node_modules/learnyounode/exer
  cises/make_it_modular/solution/solution_filter.js_ :  

     var fs = require('fs')
     var path = require('path')  

     module.exports = function (dir, filterStr, callback) {  

       fs.readdir(dir, function (err, list) {
         if (err)
           return callback(err)  

         list = list.filter(function (file) {
           return path.extname(file) === '.' + filterStr
         })  

         callback(null, list)
       })
     }