Setting Session variables in Client SuiteScript

All, we are still working on our custom NetSuite form.  We have a pop-up window that will communicate with the main window by accessing and modifying variables stored in the nlobjContext object's session parameter.  We have no problem creating and accessing the session variables on the server side, but client script that runs the context.setSetting('SESSION') function fail.  The exact error message is "context.setSetting is not a function".  If we cannot modify the session variable in client suitescript, is there a way to pass data from the pop-up window without submitting the page?  We need the pop-up window to close itself