A simple counter in javascript?

Question

var points;

function add()
{
points++;
}

add();
add();
alert(points);

function add2(points)
{
points ++;
}

add2(points);
add2(points);
alert(points);

Why does each alert output NaN?
How do you make a counter in JavaScript? The scope is unlike other languages. I've heard of hoisting, but I'm not sure if I completely understand it.

Answer 1

Yes that's correct...😂
Or undefined + number = undefined
The point is that if you don't put a value to your variable, it automatically becomes undefined.

Answer 2

In the future, can you embed a code playground code to the question, making it easier for us to debug your code.

Answer 3

My apologies, here is an example:

https://code.sololearn.com/W9O9il74I8kc/?ref=app

Answer 4

I see, so I just needed to initialize it. So I guess NaN + some number = NaN?

Answer 5

Thank you!

Answer 6

There it is. You should had initialized your variable points like in the code.

https://code.sololearn.com/W3t2Pir9kXHK/?ref=app