html classlist has code example
Example 1: classList has class
if (document.body.classList.contains('thatClass')) {
// do some stuff
}
Example 2: classlist.contain in javascript
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'";
}