Javascript Interview Question:Operation on undefined variable

consider code snippet below

Code:

x++;

console.log(x);

var x = 21;

Output:

NaN

Explanation:

Here we are doing mathematical operation on undefined hence NaN.

Code Snippet 2:

Code :

var x = 23;

(function () {

var x = 43;

(function random() {

x++;

console.log(x);

var x = 21;

})();

})();

Output:

NaN

Explanation:

Here two Immediately Invocable functions are nexted inside one another.

In top IIFE x is defined again using var.

In IIFE nexted inside again x is defined using var.

So here due to Hoisting behaviour code line above it get value of x as undefined.

on the first line we are doing mathematical operation on undefined so x become NaN.

the code line after that

console.log(x)

prints

NaN