How can assign multiple css classes to an html element through javascript without using any libraries?
There are at least a few different ways:
var buttonTop = document.getElementById("buttonTop");
buttonTop.className = "myElement myButton myStyle";
buttonTop.className = "myElement";
buttonTop.className += " myButton myStyle";
buttonTop.classList.add("myElement");
buttonTop.classList.add("myButton", "myStyle");
buttonTop.setAttribute("class", "myElement");
buttonTop.setAttribute("class", buttonTop.getAttribute("class") + " myButton myStyle");
buttonTop.classList.remove("myElement", "myButton", "myStyle");