JavaScript Variables

Introduction to Variables

You can declare JavaScript variables using var, let, or const..

Declaring Variables:

• var: Older way, function-scoped
• let: Modern way, block-scoped
• const: Block-scoped and cannot be reassigned

var name = "Alice";
let age = 25;
const country = "India";
            

Variable Naming Rules:

• Names can contain letters, digits, underscores, and dollar signs
• Names must begin with a letter, underscore (_), or dollar sign ($)
• Names are case sensitive
• Reserved words cannot be used as names
• Must begin with a letter, _, or $
• Case sensitive (name and Name are different)
• Cannot be a reserved keyword (like let, if, etc.)

Reassigning Variables

Only var and let variables can be reassigned.

let score = 50;
score = 100; // Valid

const pi = 3.14;
pi = 3.14159; // ❌ Error: Assignment to constant variable
            

Scope of Variables

• Global Scope: Declared outside functions – accessible everywhere
• Function Scope: Declared inside a function – accessible only within it
• Block Scope: let and const inside { }

function example() {
  var a = 10;
  let b = 20;
  const c = 30;
}
console.log(a); // ❌ Error: a is not defined
            

Best Practices

• Use let and const instead of var
• Prefer const when the variable does not change
• Choose meaningful variable names

Practice Task

Create a variable for your name, age, and country, and display them using alert():

let name = "John";
let age = 21;
let country = "India";

alert("Name: " + name + "\nAge: " + age + "\nCountry: " + country);