JavaScript var, let, const

Difference between var, let and const

Feature	var	let	const
Scope	Function/Global	Block	Block
Hoisting	Yes, initialized with undefined	Yes, not initialized	Yes, not initialized
Reassignment	Allowed	Allowed	Not allowed
Initialization	Optional	Optional	Required

Here are examples demonstrating the use of var, let, and const in JavaScript:

var

The var keyword is function-scoped or globally scoped if declared outside a function. Variables declared with var can be re-declared and updated.

var name = “Alice”;
console.log(name); // Output: Alice

var name = “Bob”; // Re-declared
console.log(name); // Output: Bob

name = “Charlie”; // Updated
console.log(name); // Output: Charlie

let

The let keyword is block-scoped, meaning it is only accessible within the block it is declared in. Variables declared with let can be updated but not re-declared within the same scope.

let age = 25;
console.log(age); // Output: 25

age = 26; // Updated
console.log(age); // Output: 26

// Block scope
if (true) {
    let age = 30;
    console.log(age);// Output: 30 (inside block)
}

console.log(age); // Output: 26 (outside block)

const

The const keyword is also block-scoped. Variables declared with const cannot be updated or re-declared. However, if the variable is an object or array, the properties or elements can
be modified.

const pi = 3.14;
console.log(pi); // Output: 3.14

pi = 3.14159; // Error: Assignment to constant variable.

// Block scope
if (true) {
    const pi = 3.14159;
    console.log(pi);// Output: 3.14159 (inside block)
}

console.log(pi); // Output: 3.14 (outside block)

• var: Function or globally scoped, can be re-declared and updated.

• let: Block-scoped, can be updated but not re-declared within the same scope.

• const: Block-scoped, cannot be updated or re-declared, but object properties and
  array elements can be modified.

Each keyword has its own specific use case depending on the scope and mutability requirements of the variable.