2. Variables in JavaScript

What Are Variables?

Variables are containers that store data values. Think of them as labeled boxes that hold information your program can read or change.

let name = "Chrise";
let age = 25;
console.log(name);
console.log(age);

Declaring Variables

You can declare variables using var, let, or const. In modern JavaScript, we mostly use let and const because they behave more predictably.

var city = "Lagos";   // Old way
let score = 90;        // New and flexible
const country = "Nigeria"; // Fixed value

Use let when the value might change, and const when it should never change. var is mostly avoided now because it can create confusing scope issues.

Variable Naming Rules

• Names can contain letters, digits, underscores, and dollar signs.
• They must begin with a letter, underscore, or dollar sign.
• They are case-sensitive (age and Age are different).
• Use meaningful names like userName, not x.

Reassigning Values

let score = 10;
score = 20;
console.log(score); // 20

const variables can’t be reassigned. Trying to do so will cause an error.

const country = "Nigeria";
country = "Ghana"; // ❌ TypeError

Mini Challenge

Create a variable for your favorite programming language, print it to the console, then change it and print again.

Key Takeaway

Use let for flexible values and const for fixed ones. Avoid var unless you specifically need older JavaScript compatibility.

MDN: Declaring Variables