How I feel your pain !
Like many, I found it hard to get to the essence of Node.js because most people only write/talk about the part of Node that they find useful - and the part they find interesting is usually a secondary benefit of Node rather than its primary purpose. I must say that I think it's mad for people to say that Node is just a JavaScript runtime. Node's use of JavaScript - and its selection of the V8 runtime - are simply means to an end, the best tools for the problem that Node's developers wanted to solve.
Node's primary purpose was to make the management of user events in a web app more efficient. So Node is overwhelmingly used on the back end of a web app. Event management demands that something is listening at the server machine for these user events. So a http server must be set up to route each event to its appropriate handler script. Node provides a framework for quickly setting up a server to listen on a dedicated port for user requests. Node uses JavaScript for event handling because JavaScript allows functions to be called as objects. This allows the task to be executed immediately after an asynchronous request (e.g. to a file system, database or network) to be wrapped in a function and referenced as a parameter of the asynchronous request function call.
const mysql = require('mysql2');
const conn = mysql.createConnection(
{
host: "XXXXXXXXXXXXX",
database: "doa_statsbase",
user: "uoalabama_doas",
password: "*************"
});
. . .
. . .
const analyse_bigwheat_farmers = (err, result, fields) =>
{
. . . . .
. . . . .
return data_object;
}
. . .
. . .
let query = "SELECT * FROM us_farmers WHERE acreage > '1000' AND crop='wheat'";
mysql.query(query, (err, result, fields) =>
{
analyse_bigwheat_farmers(err, result, fields);
}
. . .
. . .
. . .
Not many other languages treat functions as objects and those that do may not have an interpreter as efficient as Google's V8 runtime. Most web developers already know JavaScript so there's no additional language learning with Node. What's more, having callback functions allows all user tasks to be put on a single thread without having explicit blocking applied to tasks demanding access to the database or file system. And this is what leads to the superior executional efficiency of Node under heavy concurrent use - the primary purpose for its development.
Today, most Node web applications use callbacks sparingly as JavaScript ES6 introduced the Promise construct in 2015 to handle asynchronous calls more easily and readably.
To help Node users quickly write back end code, Node's developers also organized both a built-in JS library for routine tasks (e.g. matters related to HTTP requests, string (de)coding, streams etc) and the NPM (Node Package Manager) repositary: this is an open source, user-maintained set of script packages for various standard and custom functions. All Node projects allow importation of NPM packages into a project via the established npm install command.
User requests handled via Node will be things needed by the web app like authentication, database querying, content management system (ApostropheCMS, Strapi CMS) updates, etc. All these will be sent to the Node port. (Where analysis of data got from a database is takes a lot of CPU time, this type of process is best put on a separate thread so it doesn't slow simpler user requests.) Other types of user request, e.g. to load another webpage, download CSS/JS/image files, etc, will continue to be sent by the browser to the default ports (typically ports 80 (HTTP) and 443 (HTTPS) on the server machine where the web server program (Apache, NGinx, etc) will handle them in the mode of a traditional website.
[A side note here on request streaming to the server. Since most server machines' firewalls only allow the default ports 80/443 open, it is not usually allowed to directly send a Node.js request with another port in the URL, e.g. https://mynodeapp.com:3001/fetch-members. If one did, the server machine's firewall would simply ignore it as it directly references an illegal port.
Instead one could apply a URL to the request that has no explicit port number but which contains a virtual folder name that identifies the Node.js app, e.g. https://mynodeapp.com/mynodeapp/fetch-members. Then append some server directive code on the .htaccess file like:
RewriteEngine On
RewriteRule ^mynodeapp/(.*) https://localhost:3001/$1 [P]
Node.js requests given URLs in this way will thus find their way to the Node.js server for that web app via the nominated ports for the Node application, i.e. 3001 in the example here.]
So, in practice, Node is principally a framework for rapid server-creation and event-handling but one that replaces only some of the functions of the web server program.
Other non-backend uses of Node simply exploit one or other of its features, e.g. the JavaScript V8 engine. For example, the frontend build tools Grunt and Gulp use a frontend Node.js app to process a build script that can be coded to convert SASS to CSS, minify CSS/JS files, optimize image size or image loading, generate page-state HTML files for refreshing page-states in a single page application site, etc. But this sort of work is really just a by-product use of Node and not its principal use which is for making efficient backend processes for modern web applications.
