Clean and simple:
window.addEventListener("wheel", event => console.info(event.deltaY));
Browsers may return different values for the delta (for instance, Chrome returns +120
(scroll up) or -120
(scroll down). A nice trick to normalize it is to extract its sign, effectively converting it to +1
/-1
:
window.addEventListener("wheel", event => {
const delta = Math.sign(event.deltaY);
console.info(delta);
});
Reference: MDN.