How can I get the browser's scrollbar sizes?

Question

How can I determine the height of a horizontal scrollbar, or the width of a vertical one, in JavaScript?

Answer 1

function getWindowScrollBarHeight() {
    let bodyStyle = window.getComputedStyle(document.body);
    let fullHeight = document.body.scrollHeight;
    let contentsHeight = document.body.getBoundingClientRect().height;
    let marginTop = parseInt(bodyStyle.getPropertyValue('margin-top'), 10);
    let marginBottom = parseInt(bodyStyle.getPropertyValue('margin-bottom'), 10);
    return fullHeight - contentHeight - marginTop - marginBottom;
  }