const pageHeight = Math.max(
document.body.scrollHeight, document.documentElement.scrollHeight,
document.body.offsetHeight, document.documentElement.offsetHeight,
document.body.clientHeight, document.documentElement.clientHeight
);
const slider = document.querySelector('.slider');
const lastIdx = slider.slick["$slides"].length - 1;
const lastSlide = slider.slick["$slides"][lastIdx];