put new attribute on html tag using javascript

1	// Selecting the element
2    var btn = document.getElementById("myBtn");
3	
4    // Setting new attributes
5    btn.setAttribute("class", "click-btn");
6    btn.setAttribute("disabled", "");

1// Here's what you do for the style attribute
2span.setAttribute("style", "width:110%;float:center;left-margin:-10px;top-margin:-10;");

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