In developer mode worked great. Later in CMD, I sent "npm run build. Got error...

info  - Checking validity of types
info  - Creating an optimized production build
info  - Compiled successfully

> Build optimization failed: found pages without a React Component as default export in
pages/js/TimeClock
pages/js/ChangePage

I tried to fix it. Nothing on the internet helped. Here are my files:

index.js

import Head from 'next/head'
import Time from './js/TimeClock.page';
import { ChangePage0, ChangePage1, ChangePage2 } from './js/ChangePage.page';

export default function Home() {
  ...
}

TimeClock.page.js

import ReactDOM from 'react-dom'

export function tick()
{
    const site = (
        <div>
            <span className="time">
                {new Date().toLocaleTimeString()}
            </span>
        </div>
    );
    ReactDOM.render(site, document.getElementById('time'));
}
setInterval(tick, 1000);

next.config.js

/** @type {import('next').NextConfig} */
const nextConfig = {
  reactStrictMode: true,
}

module.exports = {
  pageExtensions: ['page.tsx', 'page.ts', 'page.jsx', 'page.js'], nextConfig
}