I’m from python and I’m struggling to get JS basic in terms of scopes and closures.

I’m faced with a tricky moment using forEach loop.

let args = [{},null,"3"]

Case #1

var argumentsLength = function(...args) {

    let counter = 0;

    args.forEach((_) => {
        counter++;
    });

    return counter;
};

Result: 4

Case #2

let counter = 0;

var argumentsLength = function(...args) {
   
    args.forEach((_) => {
        counter++;
    });

    return counter;
};

Result: 3

In case #2, I had an extra executing of a increment operator. This is because of variable “`counter“`, but what the difference between declarating variables in block and outside the block. How does it work? And what I’ve to read to get this concept.