How to Know Which HTML Element is Causing Vertical Scroll Bar

Question

I am learning Bootstrap. On the getting started menu, there are few templates given. I am playing with that. One example is about fixed Footer. I used nav from previous example

Answer 1

Paste the below in the console and scroll. It will log the culprit in the console.

function findScroller(element) {
    element.onscroll = function() { console.log(element)}

    Array.from(element.children).forEach(findScroller);
}

findScroller(document.body);