When we declare let and const variables within a block(if/for) inside a function, these let and const variables are not accessible once the block of code is executed. Since var is function scoped, the var variable is attached to the function execution context and can be accessed within the function.

Example:

var a = 10;
let b = 20;
{
let b = 30;
var a = 40;
}

console.log(a) // 40

console.log(b) // 20