mdn add class code example

Example 1: classList has class

if (document.body.classList.contains('thatClass')) {
    // do some stuff
}

Example 2: class declaration in javascript

class NameOfClass {
//class declaration first letter should be capital it's a convention
  obj="text";
  obj2="some other text";
}
//always call class with "new" key word
console.log(new NameOfClass);