Node.js file uploading using Formidable - events are not getting fired - node.js

Question

I am trying to make a file upload using Node.js and the Formidable module.
npm install formidable
And then I made this, please read the notes - where I can explain what each function does and describes the algorithm:
// get access to the files that were sent;
// at this time I don't want the files to be uploaded yet;
// in the next function I will validate those files.
function form_parse() {
form.parse(req, (err, fields, files) => {
if (err) return req.Cast.error(err);
if (Object.keys(files).length==0) return req.Cast.badRequest();
req.files = files;
return validate_files();
});
}
// I made an object with options to validate against the
// files. it works and continues to the process_files()
// function only whether files are verified.
function validate_files() {
let limitations = require('../uploads-limitations');
try {
limitation = limitations[req.params.resource];
} catch(err) {
return req.Cast.error(err);
}
let validateFiles = require('../services/validate-files');
validateFiles(req, limitation, err => {
if (err) return req.Cast.badRequest(err);
return process_files();
});
}
// here is the problem - form.on doesn't get fired.
// This is the time I want to save those files - after
// fully verified
function process_files() {
form.on('file', function(name, file) {
console.log(`file name: ${file.name}`);
file.path = path.join(__dirname, '../tmp_uploads/' + file.name);
});
form.on('error', err => {
return req.Cast.error(err);
});
form.on('end', () => {
console.log(`successfully saved`);
return req.Cast.ok();
});
}
form_parse();
As you can see and as I have described - the validation works but when I want to actually save those files the form.on (events) are not getting fired.

Answer 1

Yes because at the end of your process, after parsing and validating, you attach events listeners. This should be done first, before starting parsing. Because these events (on file, on error, on end) happen during the parsing, not after.
form.on('file',...) // First, attach your listeners
.on('error', ...)
.on('end', ...);
form.parse(req) // then start the parsing