fix(svelte-query): handle shrinking createRawRef array by multiple entries (#10341)

.changeset/fix-svelte-query-shrink-array.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/svelte-query': patch
+---
+
+Fix `createQueries` crashing with `TypeError: 'deleteProperty' on proxy: trap returned falsish for property 'N'` when two or more items were removed from its reactive array in the same update.

packages/svelte-query/src/containers.svelte.ts

@@ -80,14 +80,24 @@ export function createRawRef<T extends {} | Array<unknown>>(
         }
         return true
       }
-      return false
+      // Spec semantics: deleting a missing prop is a no-op. Returning false here
+      // makes `delete` throw in strict mode, which broke #10341 when `update()`
+      // iterated stale indices over an already-shrunk array.
+      return true
     },
   })
 
   function update(newValue: T) {
     const existingKeys = Object.keys(out)
     const newKeys = Object.keys(newValue)
     const keysToRemove = existingKeys.filter((key) => !newKeys.includes(key))
+    // Arrays: delete in descending index order so each `deleteProperty` trap
+    // sees the slot it is removing as the current tail (length-- stays valid).
+    // Forward iteration would shrink the array under our feet and the next
+    // index would no longer be `in target`, tripping the trap.
+    if (Array.isArray(newValue)) {
+      keysToRemove.sort((a, b) => Number(b) - Number(a))
+    }
     for (const key of keysToRemove) {
       // @ts-expect-error
       delete out[key]

packages/svelte-query/tests/containers.svelte.test.ts

@@ -198,6 +198,24 @@ describe('createRawRef', () => {
     expect(ref).toEqual([7, 8, 9])
   })
 
+  it('should handle shrinking an array by more than one entry at once', () => {
+    // Regression for #10341: createQueries crashed with
+    // `TypeError: can't delete property 'N': proxy deleteProperty handler returned false`
+    // when two or more items were removed from the reactive array in a single update.
+    const [ref, update] = createRawRef([1, 2, 3, 4, 5])
+
+    expect(ref).toEqual([1, 2, 3, 4, 5])
+
+    update([1, 2])
+    expect(ref).toEqual([1, 2])
+
+    update([1, 2, 3, 4])
+    expect(ref).toEqual([1, 2, 3, 4])
+
+    update([])
+    expect(ref).toEqual([])
+  })
+
   it('should behave like a regular object when not using `update`', () => {
     const [ref] = createRawRef<Record<string, unknown>>({ a: 1, b: 2 })