Calculate the size of scrollbar

const scrollbarWidth = document.body.offsetWidth - document.body.clientWidth;

const calculateScrollbarWidth = function () {
    // Create the parent element
    const outer = document.createElement('div');
    outer.style.visibility = 'hidden';
    outer.style.overflow = 'scroll';

    // Append it to `body`
    document.body.appendChild(outer);

    // Create the child element
    const inner = document.createElement('div');
    outer.appendChild(inner);

    // Calculate the difference between their widths
    const scrollbarWidth = outer.offsetWidth - inner.offsetWidth;

    // Remove the parent element
    document.body.removeChild(outer);

    return scrollbarWidth;
};