Busboy sending response back before reading file length and file data? i am uploading single file

Question

module.exports.upload = function (req, res) {
  fileName = path.basename(req.query.fileName);
  var fileExtn = path.extname(req.query.fileName);
  console.log("fileName " + fileName);
  console.log("fileExtn " + fileExtn);

  var fileCheckResponse = FileCheck(req, res);  // FileCheck method containing Busboy code
  console.log("file check response =" + fileCheckResponse);
}

function FileCheck(req, res) {
var dataSize;
  var busboy = new Busboy({ headers: req.headers });
    busboy.on('file', function(fieldname, file, filename, encoding, mimetype) {
      file.on("data", function (data) {
        dataSize=data.length;
      console.log("File [" + fieldname + "] got " + data.length + " bytes");
      console.log("the upload file data ===== " + data);

      })
    });
    busboy.on('finish', function() {
      console.log('Upload complete');
      return dataSize;
    });
   return  req.pipe(busboy);
}`

here from upload method i am calling FileCheck function where Busboy code is present and i put debug and check in FileCheck function first it hits the line ( busboy.on('file', function(fieldname, file, filename, encoding, mimetype) ) then it doesn't goes inside it hits another line ( busboy.on('finish', function()) then response object goes back to upload method, i am expecting datalenght in fileCheckResponse but getting object which is not containing it, again on continue debug again it goes back to FileCheck function and this time it hits ( file.on("data", function (data)) and prints data on console as i have written but response doesn't comes back to upload method.

Here again my question and goal is to get datalength as response but now first time i am getting object as response and second time pointer doesn't come back to upload method.

Answer 1

// try using const or let instead of var

module.exports.upload = function (req, res) {

  fileName = path.basename(req.query.fileName);
  const fileExtn = path.extname(req.query.fileName)
  console.log("fileName " + fileName);
  console.log("fileExtn " + fileExtn);


  // try to make FileCheck function synchronous using promise or async await

  FileCheck(req, res)
    .then(fileSize => {
        console.log(fileSize, 'fileSize')
        // send whatever response you need
    })
}

function FileCheck(req, res) {
    return new Promise((resolve, reject) => {
        let dataSize;
        let busboy = new Busboy({ headers: req.headers });
        busboy.on('file', function(fieldname, file, filename, encoding, mimetype) {
            file.on('data', function (data) {
                dataSize = data.length;
                console.log("File [" + fieldname + "] got " + data.length + " bytes");
            })
        });
        busboy.on('finish', function() {
            console.log('Upload complete');
            resolve(dataSize)
        });
        req.pipe(busboy)
    })
}