Var, Let and Const

var, let, and const are all used to declare variables in JavaScript, but they have some differences in terms of scope, reassignment, and initialization:

var

• var declarations are globally scoped or function scoped.
• They can be reassigned and re-declared within their scope.
• var variables are hoisted to the top of their scope and initialized with undefined.

var x = 10;
console.log(x); // Output: 10

{
    var x = 20;
    console.log(x); // Output: 20
}

console.log(x); // Output: 20

let

• let declarations are block scoped.
• They can be reassigned but not re-declared within their scope.
• let variables are not hoisted; they are only accessible after they are declared.

let y = 10;
console.log(y); // Output: 10

{
    let y = 20;
    console.log(y); // Output: 20
}

console.log(y); // Output: 10

const

• const declarations are block scoped.
• They cannot be reassigned or re-declared within their scope.
• const variables must be initialized during declaration and cannot be left uninitialized.

const z = 10;
console.log(z); // Output: 10

{
    const z = 20;
    console.log(z); // Output: 20
}

console.log(z); // Output: 10

In summary, var has function scope, let and const have block scope. let allows reassignment, while const does not. const requires initialization and cannot be re-declared or reassigned.

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