var element = document.getElementById("elemId"); element.setAttribute("attributeName", "value");
element.setAttribute(<name>, <value>); // ex var aElement = document.querySelector("a"); aElement.setAttribute("href", "https://isitchristmas.com/"); // same as <a href="https://isitchristmas.com/"></a>
// thats how we set attribute. document.getElementsByTagName("H1")[0].setAttribute("class", "democlass");