java header not working background

const scroller = document.querySelector(“#musicscrollid”);
const output = document.querySelector(“#musicheaderid”);

scroller.addEventListener(“scroll”, (event) => {
output.textContent = scrollTop: ${scroller.scrollTop};
if (scroller.scroll >= 64) {
output.addClass(“fondoazul”);
} else {
output.removeClass(“fondoazul”);
}
});

the output.text i see number but when i scroll 64px the addclass or removeclass is not working