Gojs example http://jsbin.com/zoxowiduna/1/edit?js,output

script.js

var $ = go.GraphObject.make;  // for conciseness in defining templates

    myDiagram = $(go.Diagram, "myDiagramDiv",  // create a Diagram for the DIV HTML element
                  {
                    initialContentAlignment: go.Spot.Center,  // center the content
                    "undoManager.isEnabled": true  // enable undo & redo
                  });

    // define a simple Node template
    myDiagram.nodeTemplate =
      $(go.Node, "Auto",  // the Shape will go around the TextBlock
        $(go.Shape, "RoundedRectangle", { strokeWidth: 0},
          // Shape.fill is bound to Node.data.color
          new go.Binding("fill", "color")),
        $(go.TextBlock,
          { margin: 8 },  // some room around the text
          // TextBlock.text is bound to Node.data.key
          new go.Binding("text", "key")),
        $(go.Shape, "Circle", {
          width: 20,
          height: 20,
          stroke: 'transparent',
          fill: 'red',
          position: new go.Point(0, 0),
          isActionable: true,
          click: function(e, b) {
            console.log('foo');
          }
        })
      );

    // but use the default Link template, by not setting Diagram.linkTemplate

    // create the model data that will be represented by Nodes and Links
    myDiagram.model = new go.GraphLinksModel(
    [
      { key: "Alpha", color: "lightblue" },
      { key: "Beta", color: "orange" },
      { key: "Gamma", color: "lightgreen" },
      { key: "Delta", color: "pink" }
    ]);
myDiagram.addDiagramListener("ChangedSelection",
function(e, obj) {
  console.log('ChangedSelection');
});