How to open an URL when clicking a node with SiGMa-core:

onClickNode.as

// To react a node clicking, you have to listen to the
// event InteractionControler.CLICK_NODES:
InteractionControler.addEventListener(InteractionControler.CLICK_NODES,onClickNodes);

function onClickNodes(e:ContentEvent):void{
  // e is a ContentEvent, with an array containing the
  // IDs of each node under the mouse cursor during the
  // click:
  var clickedNodeIDs:Array = e.content;
  
  // We suppose here that the most relevant node is the
  // last one (the one "on the top") of the array:
  var nodeID:String = clickedNodeIDs[clickedNodeIDs.length-1];

  // Graph.nodesIndex gives you the index of a node in
  // the nodes vector from its ID (Graph.nodes):
  var node:Node = Graph.nodes[Graph.nodesIndex[nodeID]];
  
  // We suppose here that the URL is contained in the attribute
  // "url" of the nodes:
  var url:String = node.attributes["url"];
  var request:URLRequest = new URLRequest(url);
  try {
    navigateToURL(request, '_blank');
  } catch (e:Error) {
    trace("An error occurred!");
  }
}