Returning output parameter from custom workflow activity to action

I have created a custom javascript rule which calls an action built in CRM. I have used SOAP request to call action from javascript.  Inside the action,I have added the custom workflow activity as a step. When I run this javascript rule,I am able to set the value of a boolean variable in the custom workflow(as intended).But,I don't know how to retrieve the output parameter from the custom workflow activity to the javascript.