JavaScript Lesson 2: Variables (var, let, const)

Variables store data. JavaScript has three ways to declare them. Knowing which one to use matters — and it’s simpler than it sounds.

let — For Values That Change

let age = 25;
let score = 0;
let userName = "Alice";

// Can change the value
age = 26;
score = score + 10;

console.log(age);    // 26
console.log(score);  // 10

const — For Values That Never Change

const PI = 3.14159;
const MAX_USERS = 100;
const SITE_NAME = "BeginnerCoder";

// PI = 3.14;  // ERROR! Cannot reassign a const

// Best practice: use const by default.
// Only use let when the value will change.

var — The Old Way (Avoid It)

var oldWay = "I am var";
// var has weird scoping issues. Do not use.
// Always prefer let or const in modern JS.

Rules for Variable Names

// JavaScript uses camelCase (not snake_case like Python)
let firstName = "Alice";   // camelCase
let totalScore = 100;
let isLoggedIn = true;

// Rules:
// - Start with letter, $, or _
// - No spaces
// - Case sensitive (name !== Name)

let name = "Alice";
let Name = "Bob";    // different variable!

console.log() — Your Best Friend

let x = 10;
let y = 20;
let sum = x + y;

console.log(sum);           // 30
console.log("Sum is:", sum); // Sum is: 30
console.log(x, y, sum);     // 10 20 30

// Use template literals (backtick strings)
console.log(`${x} + ${y} = ${sum}`);  // 10 + 20 = 30