refactor(internals): use non enumerable props

src/types/nodes.ts

@@ -2,6 +2,7 @@ import { CSSProperties, MouseEvent as ReactMouseEvent } from 'react';
 
 import { XYPosition, Position, CoordinateExtent } from './utils';
 import { HandleElement } from './handles';
+import { handleBoundsSymbol, isParentSymbol, zSymbol } from '../utils';
 
 // interface for the user node items
 export interface Node<T = any> {
@@ -28,9 +29,9 @@ export interface Node<T = any> {
 
   // only used internally
   positionAbsolute?: XYPosition;
-  z?: number;
-  handleBounds?: NodeHandleBounds;
-  isParent?: boolean;
+  [zSymbol]?: number;
+  [handleBoundsSymbol]?: NodeHandleBounds;
+  [isParentSymbol]?: boolean;
 }
 
 // props that get passed to a custom node