How to handle large file processing through AJAX and express - node.js

Question

I'm uploading a PDF file using AJAX and express and sending the data to external REST API for some file processing.
Whenever I upload more than 3MB file I will get an error in AJAX before the REST API response.
I get correct results from the external REST API, but processing takes more time so AJAX is not receiving the success msg.
How do I handle this?
Tried with AXIOS and other promise handler but same result
module.exports = (req, res) =>
{
var pdf = [],
form = new formidable.IncomingForm(),
pdfFile,
dirname = process.cwd();
form.multiples = false;
// Upload directory for the images
form.uploadDir = path.join(dirname, 'tmp_uploads');
form.on('file', function(name, file) {
let token;
console.log('FORM ON')
if (req.cookies.userData.token) {
token = req.cookies.userData.token;
let buffer = null,
type = null,
filename = '',
renameFile = '';
// Read a chunk of the file.
buffer = readChunk.sync(file.path, 0, 262);
// filename = Date.now() + '-' + file.name;
filename = file.name;
renameFile = path.join(dirname, 'uploads/' + filename);
fs.rename(file.path, renameFile, function(err) {
if (err) throw err;
console.log('renamed complete');
pdfFile = path.join(dirname, 'uploads/' + filename);
let readFileStream = fs.createReadStream(pdfFile),
data = '',
formData = {};
formData = {
name: filename,
my_file: readFileStream,
Width: 1024,
Height: 768
};
function postData() {
// Setting URL and headers for request
var options = {
url: EXTERNALURL,
headers: {
"Authorization": 'bearer ' + token,
"content-type": "multipart/form-data"
},
formData: formData
};
// Return new promise
return new Promise(function(resolve, reject) {
// Do async job
request.post(options, function(err, resp, body) {
if (err) {
reject(err);
} else {
resolve(body);
}
})
})
}
function getData(url) {
// Return new promise
return new Promise(function(resolve, reject) {
// Do async job
request.get({ url: url, encoding: null }, function(err, resp, body) {
if (err) {
reject(err);
} else {
resolve(body);
}
})
})
}
var errHandler = function(err) {
console.log(err);
}
var filePath;
function main() {
var dataPromise = postData();
// Get user details after that get followers from URL
dataPromise.then(JSON.parse, errHandler)
.then(function(result) {
fData = result;
var fileName = fData.Id,
file_url = fData.PresentationZipUrl;
filePath = path.join(dirname, fData.HtmlPath);
// Do one more async operation here
var downloadPromise = getData(file_url).then();
return downloadPromise;
}, errHandler)
.then(function(data) {
//console.log(data);
var zip = new AdmZip(data);
if (!fs.existsSync(filePath)) {
fs.mkdirSync(filePath);
zip.extractAllTo(filePath, true);
}
}, errHandler)
.then(function(data) {
console.log('Done');
res.status(200).json({ 'status': "success" });
}, errHandler);
}
// console.log('before');
main();
}); // END RENAME FILE
} else { //
console.log('ERROR')
res.redirect('/');
}
});
form.on('error', function(err) {
console.log('Error occurred during processing - ' + err);
});
// Invoked when all the fields have been processed.
form.on('end', function() {
console.log('All the request fields have been processed.');
});
// Parse the incoming form fields.
form.parse(req, function(err, fields, files) {})}
AJAX:
$.ajax({
enter code here
url: '/presentation/uploadFiles',
method: 'post',
data: formData,
processData: false,
contentType: false,
timeout: 0}).done(function(d) {
console.log(d);
if (d.status == 'success') {
location.reload()
}}).fail(function(e, t) {
console.log(e);
console.log(t)})
.always(function() {
});