JSFiddle - React, Tailwind, and code Playground

JavaScript

var obj = {
                className: "math lol"
          }

function addClass(obj, cls){
    alert(obj.className.split(' '));
    if(!(cls in obj.className.split(' '))) {
        obj.className = obj.className.split(' ');
        obj.className.push(cls);
    }
}

addClass(obj, 'PH');
alert(obj.className);