add class with JavaScript

Question

I am writing some vanilla JavaScript to create a nice navigation menu. I am stuck on adding an active class.

I am getting elements by class name NOT by id. The belo

Answer 1

getElementsByClassName() returns HTMLCollection so you could try this

var button = document.getElementsByClassName("navButton")[0];

Edit

var buttons = document.getElementsByClassName("navButton");
for(i=0;buttons.length;i++){
   buttons[i].onmouseover = function(){
     this.className += ' active' //add class
     this.setAttribute("src", "images/arrows/top_o.png");
   }
}