javaScript проверяет, есть ли у элемента класс
if(document.getElementById("myElmentID").classList.contains("hidden")){
// I have the 'hidden' class
}
Grepper
if(document.getElementById("myElmentID").classList.contains("hidden")){
// I have the 'hidden' class
}element.classList.contains(className);element.classList.contains(class);let span = document.querySelector("span");
let classes = span.classList;
let result = classes.contains("d");
if (result) {
span.textContent = "The classList contains 'c'";
} else {
span.textContent = "The classList does not contain 'c'";
}