javascript add class to element based on id 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: add class to html tag javascript

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

root.className += ' responsive';