javascript change attribute

1var element = document.getElementById("elemId");
2element.setAttribute("attributeName", "value");

1element.setAttribute(<name>, <value>);
2// ex
3var aElement = document.querySelector("a"); 
4aElement.setAttribute("href", "https://isitchristmas.com/"); 
5// same as <a href="https://isitchristmas.com/"></a>

1Element.setAttribute(name, value);

1//Fetch id from html
2var a = document.getElementById("id");
3
4//variable.setAttribute("Attributes","Properties:Values")
5a.setAttribute("style", "visibility:hidden;");
6

1
2 document.getElementsByTagName("H1")[0].setAttribute("class", "democlass");