Express-validator does not "see" my form fields

When the client sends a form with multipart/form-data encoding, the express-validator "check" middleware-chain do not "see" the form fields, let alone validate them. Is it supposed to work with some parsing middleware I'm not aware of or did I miss something? Without the validator, formidable below successfully "sees" and extracts the fields. I've read the express-validator README one too many times without any solution.

const express = require('express');
const router = express.Router();
const formidable = require('formidable');
const bcrypt = require('bcryptjs');
const mysql = require('mysql');
const uuid = require('uuid/v4');
const { check, validationResult } = require('express-validator/check');

router.post('/files', function () {
//Handle profile picture uploads here. End request;
});

//Sanitize, validate. Ends req if err
// noinspection JSUnresolvedFunction
router.post("/",[
check('alias')
    .exists() 
    .withMessage("ER_NO_ALIAS_FIELD") //Message is returned in result yet formidable
    .not()                            //below is able to extract the fields
    .isEmpty()                        //Proves that express-validator doesn't "see"
    .withMessage("ER_NO_NAME")        //the fields.
    .isFullWidth()
    .withMessage('ER_NAME_HALF_WIDTH')
    .escape()
    .trim(),
check('email')
    .exists()
    .withMessage("ER_NO_EMAIL_FIELD") //Message is returned
    .not()
    .isEmpty()
    .withMessage('ER_NO_EMAIL')
    .isEmail()
    .withMessage('ER_EMAIL_FORMAT')
    .trim()
    .normalizeEmail(),
check('sex')
    .isIn(['M', 'F'])
    .withMessage('ER_SEX'),
check('dob')
    .not()
    .isEmpty()
    .withMessage('ER_NO_DOB'),
check('pref')
    .not()
    .isEmpty()
    .withMessage('ER_NO_PREF'),
check('about')
    .not()
    .isEmpty()
    .withMessage("ER_NO_ABOUT") //To prevent the subsequent errors from being sent. Works because of "onlyFirstError: true"
    .isLength({max: 255})
    .withMessage('ER_ABOUT_LENGTH')
    .isFullWidth()
    .withMessage('ER_ABOUT_HALF_WIDTH')
    .trim()
    .escape(),
check('school')
    .not()
    .isEmpty()
    .withMessage("ER_NO_SCHOOL") //To prevent the subsequent errors from being sent. Works because of "onlyFirstError: true"
    .isFullWidth()
    .withMessage("ER_SCH_HALF_WIDTH")
    .isLength({max: 255})
    .withMessage("ER_SCH_LENGTH")
    .trim()
    .escape(),
check('password')
    .not()
    .isEmpty()
    .withMessage("ER_NO_PASSWD")
], (req, res)=>{
//Check the validation result here
let result = validationResult(req);
if(result.isEmpty()) {
    next();
} else {
    //Format the errors and echo them back to the client
    //The query ends here
    res.writeHead(200, {'Content-Type':'text/html', 'Access-Control-Allow-Origin': 'http://localhost:3000'});
    res.write("<?xml version='1.0' encoding='UTF-8' ?>");
    res.write(`<cookie>${res.getHeader('Set-Cookie')}</cookie>`); //DEV

    //Return an array of validation results/errors. Only the first error
    let error_array = result.array({onlyFirstError: true});

    res.write(`<err_arr>${JSON.stringify(error_array)}</err_arr>`);
    res.write("<msg>There was a problem with the form entries</msg>");

    res.end("<srv_res_status>8</srv_res_status>");
}
});

router.post('/', function (req, res) {
res.writeHead(200, {'Content-Type':'text/html', 'Access-Control-Allow-Origin': 'http://localhost:3000'});
res.write("<?xml version='1.0' encoding='UTF-8' ?>");
let form = new formidable.IncomingForm();
form.parse(req, (err, fields, files)=>{
    if(err) throw err;
    //fields contains the form fields

As mentioned in formidable's README, "This is a low-level package". Therefore suitable for usage together with Node's http module.

You can't simply pass it as a express middleware, and the body parsing is done its own way.

Now, to the issues with your code:

1. express' "standard" body parser, body-parser, doesn't handle multipart requests. Therefore if you send anything else (urlencoded or JSON requests), express-validator will work fine.
2. You specified your validations before body parsing takes place. So when express-validator does its thing, it will see an empty req.body.
   Even if formidable worked out-of-box with express, according to your code it would be too late to validate anything.

As a side note, in my opinion a much better option in case you want to go a 100% express is multer.