Cannot send data to Node Express after converting from CJS to ESM

After having carefully converted my JS code for NodeJS from CJS to ESM (with some unexpected difficulties), I am failing to send a body content to my Node Express web server, running for test purposes on my same computer.

My project has before had success in this, both with Node Express as described, and also on the real web, run by Apache2 served by PM2 and Node Express. I have tried to follow the advices and recommendations I've found.

For the browser, this is an excerpt from the JS code at present

... var srchData = new FormData(); srchData.append("like", str); srchData.append("cols", searchWhere); ... return new Promise((resolve, reject) => { let xhr = new XMLHttpRequest(); xhr.open('POST', 'search/', true, null, null); xhr.setRequestHeader('accepts', 'application/json'); xhr.onload = function() { if (this.status >= 200 && this.status < 300) { ... } else { ... } } xhr.send(srchData); }); ...

and, for the Express server (server.js), a corresponding excerpt is

import express from 'express' ... const app = express() app.use(express.json()) export default app import routes from './app/routes.js' routes(app) ... const port = process.env.PORT || 3000 app.use('/', express.static('public')) app.listen(port)

and (app/routes.js)

import path from 'node:path' import { access, writeFile, readFile, readdir, open } from 'node:fs/promises' import fs from 'node:fs' import multer from 'multer' import bodyParser from 'body-parser' import util from 'util' ... export default function(app) { ... app.post ('/search', async function(req, res, next) { console.log("req.body =", req.body) // *prints undefined* ... }) ... } ...

The comment prints undefined is where the problem is seen.

Please tell if more information is needed in order to understand the problem.