Set message dialog icon
<html> <head> <title>Hello World Window</title> <link rel="stylesheet" type="text/css" href="ext-3.0.0/resources/css/ext-all.css" /> <script type="text/javascript" src="ext-3.0.0/adapter/ext/ext-base.js"></script> <script type="text/javascript" src="ext-3.0.0/ext-all.js"></script> </head> <body> <script type="text/javascript"> Ext.onReady(function() { var myCallback = function(btn, text) { alert('You pressed ' + btn); if (text) { alert('You entered : ' + text) } } Ext.Msg.show({ title : 'Hold on there cowboy!', msg : 'Are you sure you want to reboot the internet?', width : 300, buttons : Ext.MessageBox.YESNOCANCEL, fn : myCallback, icon : Ext.MessageBox.ERROR }) }); </script> <div id='div1'>asdf</div> </body> </html>