Code

diagram.addEventListener(Events.itemAdded,
    function (diag, event)
    {
        if (event.getItem() instanceof DiagramLink)
        {
            console.log("link added");
            console.log(event.getItem().getOrigin().getText());
            console.log(event.getItem().getDestination().getText());
        }
    });
diagram.addEventListener(
    Events.itemRemoved,
    function (diag, event)
    {
        if (event.getItem() instanceof DiagramLink)
        {
            console.log("link removed");
            console.log(event.getItem().getOrigin().getText());
            console.log(event.getItem().getDestination().getText());
        }
    });