I don’t want the connection line to have this event，thans
DiagramEvent listeners apply to the whole diagram. In the case of the “ObjectSingleClicked” DiagramEvent, that means every pickable GraphObject.
You can of course in your listener check the type of object that was clicked. In your case you could check whether e.subject.part instanceof go.Link.
The other way of handling click events is to implement GraphObject.click event handlers. That way you would specify click handlers on Nodes but not on Links.