Fix numeric key explode

.changeset/tasty-worms-sniff.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/form-core': patch
+---
+
+Fix issue with deleteField and numeric keys

packages/form-core/src/utils.ts

@@ -108,7 +108,10 @@ export function deleteBy(obj: any, _path: any) {
 
     const key = path.shift()
 
-    if (typeof key === 'string') {
+    if (
+      typeof key === 'string' ||
+      (typeof key === 'number' && !Array.isArray(parent))
+    ) {
       if (typeof parent === 'object') {
         return {
           ...parent,

packages/form-core/tests/utils.spec.ts

@@ -192,6 +192,24 @@ describe('deleteBy', () => {
     expect(deleteBy(structure, 'kids[3].name')).toEqual(structure)
     expect(deleteBy(structure, 'nonexistent[3].nonexistent')).toEqual(structure)
   })
+
+  it('should now throw an error when deleting a path with numeric keys', () => {
+    const structure2 = {
+      123: 'a',
+      b: {
+        234: 'c',
+      },
+      d: {
+        456: {
+          e: 'f',
+        },
+      },
+    }
+
+    expect(() => deleteBy(structure2, '123')).not.toThrow()
+    expect(() => deleteBy(structure2, 'b.234')).not.toThrow()
+    expect(() => deleteBy(structure2, 'd.456.e')).not.toThrow()
+  })
 })
 
 describe('makePathArray', () => {