Does Node.js web server persist loaded modules and data?

I am using node.js for the first time. It is running as a web server:

http.createServer(app).listen(process.env.PORT);

I am used to working with JS on the front-end and building all my imported modules into a single js file which is then loaded in the browser.

In my (copied sample) node.js app I find a lot of require("") e.g.

var express = require('express');

It seems that (unlike Apache which spawns multiple processes) there is only one node.js process.

Does node.js do all the requires once and then use that 'bundle' to server subsequent requests without re-requiring them?

Also does it persist variables. For example consider the following:

var day;
if (getTodayFromSystem() == 'Monday')
{
    day = 'Monday';
}

On Monday day will be Monday. But, assuming this code does stay loaded in memory, on Tuesday will day still be Monday or will it be undefined? (I used to work with mod_perl which persists loaded scripts in memory and in such as case var day would persist across requests).

Thank you

Modules are loaded and executed only once.
So if this

var day;
if (getTodayFromSystem() == 'Monday')
{
    day = 'Monday';
}

in the top level of your module you are in trouble because it will be executed only once.

If it's inside a function that is called on a HTTP request for example, you are safe.

index.js:

let idx = 2;
while (idx--) {
    const imported = require('./module.js');
    console.log(imported);
}

module.js:

console.log('exec module.js');

const test = Math.random();

module.exports = test;

The output:

exec module.js
0.18808463493203975
0.18808463493203975

Yes, Node.js uses the CommonJS module system to handle module dependencies using require().
So, if a module has been previously required during the execution of the Node.js application, the cached version will be used for subsequent requests.

Therefore, modules are loaded and initialized only once during the application startup.

Regarding variable persistence, in your example, if the variable day is assigned the value 'Monday' and the Node.js application continues to run without being restarted, the value of day will remain 'Monday' even on subsequent days unless you explicitly modify it in the code.

However, it is important to note that Node.js is designed to handle multiple requests in parallel. Each request is handled by a separate thread within the context of the single Node.js process. This means that variables declared within a request do not persist across different requests since each request is handled in isolation.
So, in your example, if the code is executed in response to a new request on Tuesday, the day variable will be undefined unless you redefine it within the logic of that specific request.

Some things I went to review here:https://nodejs.dev/en/learn/

I hope it helped...