// getting the target element
var myElement = document.querySelector('#myElement');
// example for addding some-class to the element
myElement.classList.add('some-class');
// multiple classes can be added like this
myElement.classList.add('one-class', 'one-more-class');
// example for removing any class from the element
myElement.classList.remove('any-class');var someElement= document.getElementById("myElement");
someElement.className += " newclass";//add "newclass" to element (space in front is important)element.classList.add('class');
element.classList.remove('class');// This is to add a class to any html element after you store it
// in the element variable
element.classList.add("my-class-name");
// This is to remove a class from the element
element.classlist.remove("my-class-name");
var root = document.getElementsByTagName( 'html' )[0]; // '0' to assign the first (and only `HTML` tag)
root.className += ' responsive';