JavaScript Compruebe si el elemento tiene clase
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
}
document.body.classList.contains('my-class-name')
const element = document.querySelector("#box");
element.classList.contains("active");
element.classList.contains(class);