add attribute to html code example

Example 1: set attribute javascript

Element.setAttribute(name, value);

Example 2: put new attribute on html tag using javascript

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

Example 3: set property dom javascrpt

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