dojo combobox and radio button

Question

I would like some help on how to do this task (PHP and Dojo)

Currently I have 2 dojo radio buttion and a dojo combobox. When the user click on a radio button I would like to do the followng:

1: Execute a JS/dojo function call a php method that return a json object populate the combobox with the new context and select a default value

Also, when I load the form initally rb1 should be selected and the content for the combobox should be populated

Thanks for any help