JAVASCRIPT

js set class

var element = document.getElementById('element');
element.classList.add('class-1');
element.classList.add('class-2', 'class-3');
element.classList.remove('class-3');

javascript set class of element

To change all classes for an element:
To replace all existing classes with one or more new classes, set the className attribute:

document.getElementById("MyElement").className = "MyClass";

javascript set element class

cell.className += (cell.className ? " " : "")+"current_class";