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function(req, res, next) is callback function. It's supposed to be called somewhere else, not in this snippet. In case of Express it's called by Express itself on a request with respective arguments, req, res, next.

It is impossible to tell just from looking at a file whether it is an ECMAScript Script or an ECMAScript Module. Therefore, you need to tell the engine which of the two it is.

On the web, this is solved via different MIME Types, but MIME Types don't exist on filesystems, so Node.js uses the file extension (.mjs) or the type field in package.json ("type": "module") to distinguish between the two.

As the documentation says [Note: I am quoting from the latest docs, but the only difference is whether ESM are enabled by default or not]:

Enabling

Experimental support for ECMAScript modules is enabled by default. Node.js will treat the following as ES modules when passed to node as the initial input, or when referenced by import statements within ES module code:

• Files ending in .mjs.
• Files ending in .js when the nearest parent package.json file contains a top-level field "type" with a value of "module".
• Strings passed in as an argument to --eval, or piped to node via STDIN, with the flag --input-type=module.

There are several pages more about how exactly Node.js determines whether a file is an ECMAScript Script or an ECMAScript Module.

You seem to have an outdated or somehow broken version of videojs-abloop. According to the GitHub Issues, and particularly this commit, videojs-abloop is written as an ECMAScript Module but is transpiled to an ECMAScript Script. In your case, for some reason, you have an ECMAScript Module instead of an ECMAScript Script of videojs-abloop.

Is socket the only way to make my client listen to my server?

Well, yes. a socket connection is the only way you'll have to use something like socket.io or other socket implementation to do so.

However nodejs concept is the opposite of maintaining socket connections as that can become expensive when your connections amount scale up.

I feel the better more reliable solution is to ask the server every x seconds (2-3?) "has changes been made" and if so update the view.

With that said, depending on the exact state your saving on your app this might be not viable as a solution.

The answer was right in front of my eyes! The question I have related to, namely, has the answer after all: Mongoosejs virtual populate

In order to keep the learning spirit, I shall summarize here the solution.

According to the official documentation:

I think the * endpoint in app.use() is just a wildcard saying to route all incoming requests to that code, similar to the way your / is working.

But yes, you are understanding correctly. Basically, he is saying that any middleware which makes asynchronous requests should use this wrapAsync function. You can remove the comment lines in the wrapAsync implementation if you want.

With the wrapAsync function, you can pass your own async middleware functionality into this wrapper, and it will make sure to call your async middleware and .catch() the promise to call next, so that you don't have to worry about that detail when writing code. You can simply throw errors, and then async wrapper will handle the Express requirement of calling next() when async code fails.