add isExpanded as argument to getItemString method

packages/react-json-tree/src/JSONNestedNode.tsx

@@ -176,7 +176,8 @@ export default function JSONNestedNode(props: Props) {
     data,
     itemType,
     createItemString(data, collectionLimit),
-    keyPath
+    keyPath,
+    expandedRef.current,
   );
   const stylingArgs = [
     keyPath,

packages/react-json-tree/src/types.ts

@@ -10,7 +10,8 @@ export type GetItemString = (
   data: unknown,
   itemType: React.ReactNode,
   itemString: string,
-  keyPath: KeyPath
+  keyPath: KeyPath,
+  isExpanded: boolean,
 ) => React.ReactNode;
 
 export type LabelRenderer = (