Respect addAsFirstChild in addNodeUnderParent (frontend-collective#480)

* fix(utils/addNodeUnderParent): respect addAsFirstChild when parentKey is `null`

* style(tree-data-utils): prettify

Author: manuelmager

src/utils/tree-data-utils.js

@@ -621,10 +621,15 @@ export function addNodeUnderParent({
   addAsFirstChild = false,
 }) {
   if (parentKey === null) {
-    return {
-      treeData: [...(treeData || []), newNode],
-      treeIndex: (treeData || []).length,
-    };
+    return addAsFirstChild
+      ? {
+          treeData: [newNode, ...(treeData || [])],
+          treeIndex: 0,
+        }
+      : {
+          treeData: [...(treeData || []), newNode],
+          treeIndex: (treeData || []).length,
+        };
   }
 
   let insertedTreeIndex = null;

src/utils/tree-data-utils.test.js

@@ -1145,6 +1145,20 @@ describe('addNodeUnderParent', () => {
     expect(expectedNewNode).toEqual(nestedParams.newNode);
     expect(previousChildren).toEqual(nestedParams.treeData[0].children);
   });
+
+  it('should add new node as first child under root if addAsFirstChild is true', () => {
+    const result = addNodeUnderParent({
+      ...nestedParams,
+      parentKey: null,
+      getNodeKey: keyFromKey,
+      addAsFirstChild: true,
+    });
+
+    const [expectedNewNode, ...previousTreeData] = result.treeData;
+
+    expect(expectedNewNode).toEqual(nestedParams.newNode);
+    expect(previousTreeData).toEqual(nestedParams.treeData);
+  });
 });
 
 describe('insertNode', () => {