Preventing duplicate links

How to restrict duplicate links between two nodes.I apply property fromLinkableDuplicates:false and toLinkableDuplicates:false.But it is not working

The default value for GraphObject | GoJS API and GraphObject | GoJS API is false, so setting them to false will not change any behavior.

Could you be more specific about the behavior that is occurring that you do not want? A screenshot might help. Do you have more than one port on your nodes?