JavaScript: Variables & Data Types

What you will learn

How to declare variables and understand the main data types. JavaScript is dynamically typed: a variable can hold a string now and a number later.

let and const (modern)

let name = "Alice";        // can reassign later
const birthYear = 1998;    // cannot reassign
let age = 25;

let is block-scoped (visible only inside { }). const makes the binding immutable — but objects/arrays declared with const can still have their content modified:

const fruits = ["apple"];
fruits.push("banana");  // allowed
// fruits = ["cherry"]; // TypeError: assignment to constant

Avoid var

var is function-scoped and hoisted with confusing behavior. Prefer let and const in modern code.

Data types

Quick check below!