Vanilla JS: Fixed header on scroll

js_fixed_header_on_scroll.js

    let scrollpos = window.scrollY
    const headerElem = document.querySelector(".dress-details")
    const headerElemHeight = headerElem.offsetHeight
    const add_class_on_scroll = () => headerElem.classList.add("fixed")
    const remove_class_on_scroll = () => headerElem.classList.remove("fixed")
    
    window.addEventListener('scroll', function() { 
        scrollpos = window.scrollY;
        if (scrollpos >= headerElemHeight) { add_class_on_scroll() }
        else { remove_class_on_scroll() }
        console.log(scrollpos)
    })