Canvas.isModified listener is not calling?

i am doing some changes in canvas.But canvas.isModified is not calling in any specific case.can you tell me what may be the cases.

GoJS does not have a Canvas class – that is an HTML DOM interface, and it does not define an “isModified” property.

There is a Diagram.isModified property. If you want to be notified when it changes value, implement a “Modified” DiagramEvent listener. Note the documentation, Page Not Found -- Northwoods Software

do not modify the Diagram or its Model in the event listener

Ya I also calling with diagram.isModified here my diagram is canvas.its DiagramEvent listener is not calling

Perhaps it was already modified, so the property never changed value after registering the listener.

Maybe you want to establish a “ModelChanged” listener, as shown at Diagram | GoJS API. Or call Diagram | GoJS API.