NodeJS Google Drive Upload files

const fs = require('fs');
const readline = require('readline');
const {google} = require('googleapis');

// If modifying these scopes, delete token.json.
const SCOPES = [
    'https://www.googleapis.com/auth/drive.metadata.readonly',
    'https://www.googleapis.com/auth/drive.file',
'https://www.googleapis.com/auth/drive.metadata'];
// The file token.json stores the user's access and refresh tokens, and is
// created automatically when the authorization flow completes for the first
// time.
const TOKEN_PATH = 'token.json';
let files = [];
let index = -1;
let currentProcess = 0;
let limitUpload = 10;
// Load client secrets from a local file.
fs.readFile('credentials.json', (err, content) => {
  if (err) return console.log('Error loading client secret file:', err);
  // Authorize a client with credentials, then call the Google Drive API.
  authorize(JSON.parse(content), function(auth){
    
    var path = '~/Pictures/wallpapers/';
    function start(){
        setInterval(function(){
            if(currentProcess<limitUpload){
                index++;
                currentProcess++;
                console.log(index+'/'+files.length);
                let file = files[index];
                uploadFiles(auth,{
                    name:file,path:path+file
                },function(data){
                    currentProcess--;
                });
            }
        },200);
    }
    fs.readdir(path, function(err, items) {
        files = items;
        if(files)
        start();
    });
  });
});

/**
 * Create an OAuth2 client with the given credentials, and then execute the
 * given callback function.
 * @param {Object} credentials The authorization client credentials.
 * @param {function} callback The callback to call with the authorized client.
 */
function authorize(credentials, callback) {
  const {client_secret, client_id, redirect_uris} = credentials.installed;
  const oAuth2Client = new google.auth.OAuth2(
      client_id, client_secret, redirect_uris[0]);

  // Check if we have previously stored a token.
  fs.readFile(TOKEN_PATH, (err, token) => {
    if (err) return getAccessToken(oAuth2Client, callback);
    oAuth2Client.setCredentials(JSON.parse(token));
    callback(oAuth2Client);
  });
}

/**
 * Get and store new token after prompting for user authorization, and then
 * execute the given callback with the authorized OAuth2 client.
 * @param {google.auth.OAuth2} oAuth2Client The OAuth2 client to get token for.
 * @param {getEventsCallback} callback The callback for the authorized client.
 */
function getAccessToken(oAuth2Client, callback) {
  const authUrl = oAuth2Client.generateAuthUrl({
    access_type: 'offline',
    scope: SCOPES,
  });
  console.log('Authorize this app by visiting this url:', authUrl);
  const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
  });
  rl.question('Enter the code from that page here: ', (code) => {
    rl.close();
    oAuth2Client.getToken(code, (err, token) => {
      if (err) return console.error('Error retrieving access token', err);
      oAuth2Client.setCredentials(token);
      // Store the token to disk for later program executions
      fs.writeFile(TOKEN_PATH, JSON.stringify(token), (err) => {
        if (err) console.error(err);
        console.log('Token stored to', TOKEN_PATH);
      });
      callback(oAuth2Client);
    });
  });
}

function uploadFiles(auth,file,callback){
    var folderId = '17jsIawyQmbbrLCI5jq39s0FcOzl8VSVS';
    const drive = google.drive({version: 'v3', auth});
    var fileMetadata = {
        'name': file.name,
        parents: [folderId]
      };
      var media = {
        mimeType: 'image/jpeg',
        body: fs.createReadStream(file.path)
      };
      drive.files.create({
        resource: fileMetadata,
        media: media,
        fields: 'id'
      }, function (err, file) {
        if (err) {
          // Handle error
          console.error(err);
        } else {
          console.log('File Id: ', file.data.id);
          if(callback)callback(file);
        }
      });
}