From a3066581f3014aae31f2d96b96428100f1674166 Mon Sep 17 00:00:00 2001
From: Evan You <yyx990803@gmail.com>
Date: Fri, 6 Mar 2020 11:30:56 -0500
Subject: [PATCH] fix(reactivity): should not trigger length dependency on
 Array delete

close #774
---
 packages/reactivity/__tests__/reactiveArray.spec.ts | 11 +++++++++++
 packages/reactivity/src/effect.ts                   |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/packages/reactivity/__tests__/reactiveArray.spec.ts b/packages/reactivity/__tests__/reactiveArray.spec.ts
index d91d4478226..54218c19780 100644
--- a/packages/reactivity/__tests__/reactiveArray.spec.ts
+++ b/packages/reactivity/__tests__/reactiveArray.spec.ts
@@ -88,6 +88,17 @@ describe('reactivity/reactive/Array', () => {
     expect(index).toBe(1)
   })
 
+  test('delete on Array should not trigger length dependency', () => {
+    const arr = reactive([1, 2, 3])
+    const fn = jest.fn()
+    effect(() => {
+      fn(arr.length)
+    })
+    expect(fn).toHaveBeenCalledTimes(1)
+    delete arr[1]
+    expect(fn).toHaveBeenCalledTimes(1)
+  })
+
   describe('Array methods w/ refs', () => {
     let original: any[]
     beforeEach(() => {
diff --git a/packages/reactivity/src/effect.ts b/packages/reactivity/src/effect.ts
index 010aea0020a..2368caf66bd 100644
--- a/packages/reactivity/src/effect.ts
+++ b/packages/reactivity/src/effect.ts
@@ -196,7 +196,7 @@ export function trigger(
     // also run for iteration key on ADD | DELETE | Map.SET
     if (
       type === TriggerOpTypes.ADD ||
-      type === TriggerOpTypes.DELETE ||
+      (type === TriggerOpTypes.DELETE && !isArray(target)) ||
       (type === TriggerOpTypes.SET && target instanceof Map)
     ) {
       const iterationKey = isArray(target) ? 'length' : ITERATE_KEY