I want to Highlight Link Border Whenever link is Selected

I want Link Border Like These:

Please read GoJS Links -- Northwoods Software

The basic idea is to have multiple Shapes get the Link’s route by setting isPanelMain to true on each Shape. Each Shape would have a different (decreasing) strokeWidth and a different stroke.

In your case you could add a Binding to your first, thicker Shape, like this:

$(go.Shape, { isPanelMain: true, strokeWidth: 7, stroke: "transparent" },
  new go.Binding("stroke", "isSelected", s => s ? "yellow" : "transparent").ofObject())