template/html/d3-graph.js
function onNodeMouseDown(nodes, links, targetNode)
   {
      hideNodeContextMenu();

      // Only select / drag nodes with left clicked otherwise stop propagation of event.
      if (d3.event.button === 0)
      {
         selectedDragNode = targetNode;

         // Select / highlight related nodes or remove attributes based on enter state.
         fadeRelatedNodes(targetNode, true, nodes, links);
      }
      else
      {
         d3.event.stopPropagation();
      }
   }
function onNodeMouseDown(nodes, links, targetNode)
   {
      hideNodeContextMenu();

      // Only select / drag nodes with left clicked otherwise stop propagation of event.
      if (d3.event.button === 0)
      {
         selectedDragNode = targetNode;

         // Select / highlight related nodes or remove attributes based on enter state.
         fadeRelatedNodes(targetNode, true, nodes, links);
      }
      else
      {
         d3.event.stopPropagation();
      }
   }
Handles a mouse down action on a graph node. Hides any showing context menu. For left clicks the selected node
becomes the drag target and related nodes are faded. Any other mouse button is ignored.

@param {Array}    nodes - All graph nodes.
@param {Array}    links - All graph links.
@param {object}   targetNode - The target node.