Setting Up a JavaScript Environment

JavaScript can run in two very different places: inside a web browser, where it was born, and outside the browser via Node.js, which lets you run JavaScript as a standalone program the same way you would run a Python or Ruby script. Knowing how to use both environments — the browser console for quick experiments, and Node.js for real scripts and tooling — is a foundational skill before moving on to more advanced JavaScript topics.

Why it matters

JavaScript runs in two places: in the browser, where it drives web pages, and in Node.js, where it runs servers and build tools. The quickest way to learn it is to type a line and see the result at once, which is exactly what the console gives you. Being comfortable there is the first step to everything else.

Experimenting in the Browser Console

Every browser's DevTools (F12, then the Console tab) includes a live JavaScript interpreter tied to the current page. Typing an expression and pressing Enter evaluates it immediately and prints the result — no file, no setup, nothing to save. This makes the console the fastest way to test a small idea, like how Array.prototype.map behaves or what a particular date format looks like, before writing it into real code.

Installing Node.js

Node.js is a JavaScript runtime built on Chrome's V8 engine that lets JavaScript run outside any browser — on a server, in a build tool, or as a command-line script. Download the LTS (Long-Term Support) version from nodejs.org and install it; this also installs npm (Node Package Manager) automatically. Verify the install by running node -v and npm -v in a terminal, which print the installed version numbers.

Using npm and Running a Script File

npm is used to install reusable packages published by other developers (for example, npm install lodash downloads that library into a local node_modules folder) and to run project scripts defined in a package.json file. To run a plain JavaScript file directly, save it with a .js extension and run node script.js from a terminal in that folder — Node executes the file top to bottom and prints any console.log output to the terminal.

Examples

// Typed directly into DevTools Console, not saved to a file
const nums = [1, 2, 3, 4, 5];
nums.filter(n => n % 2 === 0).map(n => n * 10);

[20, 40] — the console immediately evaluates and prints the resulting array, with no file or setup needed.

// script.js
function greet(name) {
  return `Hello, ${name}! This ran outside the browser.`;
}

console.log(greet('Webnest'));
console.log('Node version check:', process.version);

Hello, Webnest! This ran outside the browser.
Node version check: v20.11.0

Exercise

Print a greeting, then print the result of a calculation to confirm that multiplication is done before addition.

Expected output: Hello, JavaScript then 14

// TODO: log the text "Hello, JavaScript"

// TODO: log the result of 2 + 3 * 4

console.log("Hello, JavaScript");

console.log(2 + 3 * 4);

Quick quiz

Interview questions