how do I make and animation start on click in js
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <style type="text/css"> .classname { -webkit-animation-name: cssAnimation; -webkit-animation-duration:3s; -webkit-animation-iteration-count: 1; -webkit-animation-timing-function: ease; -webkit-animation-fill-mode: forwards; } @-webkit-keyframes cssAnimation { from { -webkit-transform: rotate(0deg) scale(1) skew(0deg) translate(100px); } to { -webkit-transform: rotate(0deg) scale(2) skew(0deg) translate(100px); } } </style> <script type="text/javascript"> function ani(){ document.getElementById('img').className ='classname'; } </script> <title>Untitled Document</title> </head> <body> <input name="" type="button" onclick="ani()" /> <img id="img" src="clogo.png" width="328" height="328" /> </body> </html>