This is a good article but am still not able to figure out following problem.

I have a simple login page written in extension JS in following way:
Ext.onReady(function()
{
Ext.QuickTips.init();
Ext.form.Field.prototype.msgTarget = 'side';
new Ext.Button({
renderTo:'login',
text: 'Login',
width: 800
}).on('click',function()
{
document.forms[0].submit();

});
});

Now when I use selenium testing via browser I get a randomly generated id which when hard coded can very well be used in following way:
selenium.click("ext-gen26");

My concern is how to get reference of this generated id, so my selenium test case in JUnit is not dependent on randomly generated ids from Extension JS?

Your suggestions appreciated.

Regards,
Prashant