How to update the process variables of an instance using javascript in IBM BPM?

Question

Hi,

I want to update an exposed process variable for an instance from a service during the process flow using javascript in IBM BPM.

I fetched the details using "tw.system.currentProcessInstance.businessData.get(mykey)"

I tried updating using the same system api - tw.system.currentProcessInstance.businessData.put(key,value).

But this seems to be not working and it doesnt update the process variable.

I am using IBM BAW v21. Is there any alternative for this ?

Thanks