callbacks.js

'use strict';

const fs = require('fs');

exports.uploadFolder = (source, cb) => {
  fs.readdir(source, function (err, files) {
    if (err) {
      cb('Error finding files: ' + err)
    } else {
      const fileQueue = [];

      files.forEach(function (filename, fileIndex) {
        const filePath = source+'/'+filename
        // Uploading the file
        fileQueue.push(filePath)
        fs.readFile(filePath, function(err, data){
          if (err) {
            console.log('Error reading file: ' + err)
          } else {
            // Simulating file upload
            setTimeout(() => {
              fileQueue.splice(fileQueue.indexOf(filePath), 1);
              if(fileQueue.length === 0) {
                cb(null, files.length)
              }
            }, 1000)
          }
        })
      })
    }
  })
}