Answers for "add class by class name javascript"

js add class

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

javascript add class to element

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

add class to element javascript

element.classList.add('class');
element.classList.remove('class');

add class to html tag javascript

var root = document.getElementsByTagName( 'html' )[0]; // '0' to assign the first (and only `HTML` tag)

root.className += ' responsive';