hiderV2.js

var anchored = false,
    bodyH = document.querySelector('body').offsetHeight,
    footerH = document.querySelector('footer').offsetHeight,
    indexadv = document.querySelector('.indexadv'),
    indexadvH = indexadv.offsetHeight;
var indexadvFixedBottom = indexadv.getBoundingClientRect().bottom;
var breaking = bodyH - indexadvFixedBottom - footerH - 35;
var indexadvTop = bodyH - footerH - indexadvH;

window.onscroll = function() {
    // var windowH = window.outerHeight;
    // var indexadvFixedTop = parseInt(window.getComputedStyle(indexadv, null).getPropertyValue('top'));

    if (window.pageYOffset > breaking && anchored === false) {
        anchored = true;
        console.log('down');
        indexadv.style.position = 'absolute';
        indexadv.style.top = indexadvTop + 'px';
        // indexadv.style.zIndex = '1';
    } else if (window.pageYOffset <= breaking && anchored === true) {
        anchored = false;
        console.log('up');
        indexadv.style.position = '';
        indexadv.style.top = '';
        // indexadv.style.zIndex = '';
    }
};