Check class existance
<html> <head> <style> .myClass { color : #ff0000; } </style> <script type="text/javascript"> var djConfig = { baseScriptUri : "js/dojo/" }; </script> <script type="text/javascript" src="js/dojo/dojo/dojo.js"></script> <script type="text/javascript"> function f(){ alert(dojo.hasClass('myDiv', 'myClass')); } </script> </head> <body onLoad="f();"> <div class="myClass" id="myDiv">myDiv</div> </body> </html>