JavaScript Variables

Declaring Variables

You can declare variables using var, let, or const:

let age;
const pi = 3.14;
var name = "Alice";

var, let, and const

• var: function-scoped, can be redeclared
• let: block-scoped, preferred for mutable values
• const: block-scoped, used for immutable values

var x = 10;
let y = 20;
const z = 30;

Assigning Values

You can assign values during or after declaration:

let language = "JavaScript";
let score;
score = 100;

Naming Rules

• Must begin with a letter, $, or _
• Can contain letters, digits, $, _
• Case-sensitive (score and Score are different)

Reassignment Rules

let x = 5;
x = 10;   // OK

const y = 15;
y = 20;   // ❌ Error: Assignment to constant variable

Best Practices

• Use const by default for safety
• Use let when you need to reassign values
• Avoid var in modern code
• Use meaningful, camelCase names

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