How do I get a CSS class to work in my Javascript file? -

i want class show var newcaption. below javascript have linked css class.

window.onload = function() {  var caption = document.getelementsbytagname("caption"); var oldcaption = caption[0].innerhtml; var newcaption = oldcaption + "caption";  caption[0].removechild(caption[0].firstchild); caption[0].appendchild(document.createtextnode(newcaption)); 

here's css class:

.hovernode{    background-color:#ffffcc;    border: solid 1px black;    width:100px;    height:100px;    position:relative;    float:top;    font-size:10pt;    margin:5px;    padding:3px;    color:black; } 

add class caption element.

caption.classlist.add('hovernode');