What is the output of the following JavaScript code ?

निम्नलिखित जावास्क्रिप्ट कोड का आउटपुट क्या है?

<script>
var a;
document.getElementById("demo").innerHTML = a+1;
</script>

undefined

NaN

Explanation:

In the given JavaScript code:

var a;
document.getElementById("demo").innerHTML = a + 1;

The variable a is declared but not initialized, so its value is undefined.
When you try to add undefined to 1, the result will be NaN (Not a Number).

So, the correct answer is:

(D) NaN.