js add css to class code example

Example 1: javascript add class to element

var someElement= document.getElementById("myElement");
    someElement.className += " newclass";//add "newclass" to element (space in front is important)

Example 2: js add style to each class

var all = document.getElementsByClassName('someClass');
for (var i = 0; i < all.length; i++) {
  all[i].style.color = 'red';
}