JavaScript Basics: A Beginner's Guide for Absolute Newcomers

JavaScript runs in every browser on Earth and powers everything from interactive buttons to entire web apps. This guide walks you through the absolute basics — enough to start building.

Variables: let, const, var

const name = "Ada";   // can't be reassigned
let age = 30;          // can change
// avoid var in modern code

Data types

• String — "hello"
• Number — 42
• Boolean — true / false
• Array — [1, 2, 3]
• Object — { name: "Ada" }
• null and undefined

Functions

function greet(name) {
  return `Hello, ${name}!`;
}

const greetArrow = (name) => `Hello, ${name}!`;

Conditionals and loops

if (age >= 18) console.log("adult");

for (const n of [1, 2, 3]) console.log(n);

Run JavaScript right now

Open your browser, press F12, click Console, and start typing. No setup needed.