Follow the steps to implement wow.js on your wordpress theme. The events happening are when element enters viewport add a class, when it exits viewport remove class. The javascript to add on footer const shakebtn = document.querySelector('.shakebtn') const add_class_on_scroll = () => shakebtn.classList.add("testy","wow") const remove_class_on_scroll = () => shakebtn.classList.remove("testy","wow") const observer = new window.IntersectionObserver(([entry]) => [...]