Issues with linking Javascript files with Node.js and HTML

This is because you are sending the index.html file for all requests in your app.js file, ignoring the request URL.

You need to properly serve the JS files. You can take a look here for more details: https://nodejs.org/en/knowledge/HTTP/servers/how-to-serve-static-files/

Your node server is not serving your static files, it only serves one html.

You might need to set up a static file server like or programm you server to lookup GET /internals/render.js and scaleCanvas.js

You can use express for that, it has all this out of the box.

https://expressjs.com/en/starter/static-files.html

var app, server,
    express = require('express'),
    path = require('path'),
    host = process.env.HOST || '127.0.0.1',
    port = process.env.PORT || 3000,
    root = path.resolve(__dirname, '..');
 
app = express()
app.use(express.static(root + '/public'));
server = app.listen(port, host, serverStarted);
 
function serverStarted () {
    console.log('Server started', host, port);
    console.log('Root directory', root);
    console.log('Press Ctrl+C to exit...n');
}