Basic Modules ​

Since Node.js operates as a server-side JavaScript environment, its programs differ significantly from those running in browsers, particularly in the absence of security restrictions typical in browsers. Additionally, server programs must handle network requests, read/write files, and manage binary content. Therefore, Node.js comes with built-in modules designed for basic server functionalities, which cannot be executed in a browser environment because their underlying code is implemented in C/C++.

Global Object ​

In JavaScript, there is only one global object: window in browsers. In Node.js, this object is named global. The properties and methods of global differ from those of window. You can explore it in the Node.js interactive environment:

> global.console
Object [console] {
  log: [Function: log],
  warn: [Function: warn],
  dir: [Function: dir],
  time: [Function: time],
  ...
}

Process Object ​

The process object represents the current Node.js process and provides many useful details:

> process === global.process;
true
> process.version;
'v22.3.0'
> process.platform;
'darwin'
> process.arch;
'x64'
> process.cwd(); // Returns the current working directory
'/Users/michael'
> process.chdir('/private/tmp'); // Change the current working directory
undefined
> process.cwd();
'/private/tmp'

JavaScript operates on an event-driven, single-threaded model, and Node.js follows this model as well. Node.js continually executes JavaScript functions that respond to events until there are no more events to respond to, at which point it exits.

To execute code in the next event response, you can use process.nextTick():

// test.js
process.nextTick(function () {
    console.log('nextTick callback!');
});
console.log('nextTick was set!');

Running this with node test.js will produce:

nextTick was set!
nextTick callback!

This indicates that the function passed to process.nextTick() is not executed immediately but waits until the next event loop iteration.

Node.js processes handle events via the process object. For example, you can respond to the exit event with a callback:

process.on('exit', function (code) {
    console.log('about to exit with code: ' + code);
});

Determining the JavaScript Execution Environment ​

Some JavaScript code can run in both browser and Node.js environments. To determine the execution context, you can check for the existence of global variables:

if (typeof(window) === 'undefined') {
    console.log('node.js');
} else {
    console.log('browser');
}

Importing Node Modules ​

Node.js includes many built-in modules, and you can find information on all available modules in the Node.js online documentation.

For instance, to use the randomInt() function from the crypto module, you can import it in two ways:

Method 1: Using the traditional require():

const { randomInt } = require('node:crypto');
const n = randomInt(0, 100); // Random number between 0 and 100
console.log(n);

Method 2: Using the import keyword for ESM modules:

import { randomInt } from 'node:crypto';
const n = randomInt(0, 100); // Random number between 0 and 100
console.log(n);

In the following sections, we will introduce commonly used built-in modules in Node.js.