handleVisDragStart({ nodes }) {

    if (
      !nodes.length ||
      // we do not allow nodes to be dragged if not in editor mode
      // except cases physics is enabled
      !this.isDraggingAllowed(nodes)
    ) {
      return;
    }

    this.hidePopups(0, true);
    this.assignActiveStyle(nodes);
    this.setNodesMoveable(nodes, true);

    if (nodes.length === 1) {
      this.draggedNode = nodes[0];
    }
  }
Called by vis when a node is being dragged.
Vis passes an object containing event-related information.
@param {Array<Id>} nodes - Array of ids of the nodes
    that were being dragged.