animate-within-viewport.js

//animated section

function throttle(fn, wait) {
    let time = Date.now();
    return function() {
        if (time + wait - Date.now() < 0) {
            fn();
            time = Date.now()
        }
    }
}
function checkScroll() {
    var picturesSection = document.querySelector('.pictures-section');
    var picturesSectionOffset = picturesSection.getBoundingClientRect().top;
    const scrolled = wrapper.scrollTop;
    scrolled > picturesSectionOffset ? picturesSection.classList.add("animated") : picturesSection.classList.remove("animated")
}

wrapper.addEventListener("scroll", throttle(checkScroll, 300));