From 91a7db9d9fdf44a6a1af4c6938b914ef370d30ac Mon Sep 17 00:00:00 2001
From: ygj6 <yuangongji@foxmail.com>
Date: Tue, 8 Jun 2021 15:19:50 +0800
Subject: [PATCH 1/2] fix(watch): watched previous values can't be destructure
 on first fire

---
 src/apis/watch.ts       | 1 +
 test/apis/watch.spec.js | 6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/apis/watch.ts b/src/apis/watch.ts
index 3f614141..6a2b27e6 100644
--- a/src/apis/watch.ts
+++ b/src/apis/watch.ts
@@ -329,6 +329,7 @@ function createWatcher(
     // The subsequent callbacks will redirect to `callback`.
     let shiftCallback = (n: any, o: any) => {
       shiftCallback = originalCallback
+      o = isArray(n) ? [] : undefined
       applyCb(n, o)
     }
     callback = (n: any, o: any) => {
diff --git a/test/apis/watch.spec.js b/test/apis/watch.spec.js
index 33f5b626..eeb323e6 100644
--- a/test/apis/watch.spec.js
+++ b/test/apis/watch.spec.js
@@ -457,7 +457,7 @@ describe('api/watch', () => {
         template: `<div>{{obj1.a}} {{obj2.a}}</div>`,
       }).$mount()
       expect(spy).toBeCalledTimes(1)
-      expect(spy).toHaveBeenLastCalledWith([1, 2], undefined)
+      expect(spy).toHaveBeenLastCalledWith([1, 2], [])
       obj1.a = 2
       obj2.a = 3
 
@@ -491,7 +491,7 @@ describe('api/watch', () => {
         template: `<div>{{a}} {{b}}</div>`,
       }).$mount()
       expect(spy).toBeCalledTimes(1)
-      expect(spy).toHaveBeenLastCalledWith([1, 1], undefined)
+      expect(spy).toHaveBeenLastCalledWith([1, 1], [])
       vm.a = 2
       expect(spy).toBeCalledTimes(1)
       waitForUpdate(() => {
@@ -553,7 +553,7 @@ describe('api/watch', () => {
         },
       })
       expect(spy).toBeCalledTimes(1)
-      expect(spy).toHaveBeenLastCalledWith([1, 1], undefined)
+      expect(spy).toHaveBeenLastCalledWith([1, 1], [])
       vm.a = 2
       expect(spy).toBeCalledTimes(2)
       expect(spy).toHaveBeenLastCalledWith([2, 1], [1, 1])

From 2dc71453e4a02a5c7500e70407b593b93d0b24ae Mon Sep 17 00:00:00 2001
From: ygj6 <yuangongji@foxmail.com>
Date: Tue, 8 Jun 2021 20:40:24 +0800
Subject: [PATCH 2/2] update the implementation mode

---
 src/apis/watch.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/apis/watch.ts b/src/apis/watch.ts
index 6a2b27e6..c3cb5a88 100644
--- a/src/apis/watch.ts
+++ b/src/apis/watch.ts
@@ -329,8 +329,8 @@ function createWatcher(
     // The subsequent callbacks will redirect to `callback`.
     let shiftCallback = (n: any, o: any) => {
       shiftCallback = originalCallback
-      o = isArray(n) ? [] : undefined
-      applyCb(n, o)
+      // o is undefined on the first call
+      applyCb(n, isArray(n) ? [] : o)
     }
     callback = (n: any, o: any) => {
       shiftCallback(n, o)