.classList

var myElement = document.getElementById("myElementID");
myElement.classList.add("style1 style2");
myElement.classList.remove("style1 style2");// .classList method returns an array of the classes attached to the element it is called with.
document.getElementById("myDIV").classList
// It returns
// [ 'className1', 'className2', ... ]//get array of classes in Javascript
var classesArray = document.getElementById('myElementID').className.split(/\s+/);

//get array of classes in jQuery
var classesArray = $('#myElementID').attr('class').split(/\s+/);