From ff35f0b98c3ecc3e37e1680b1d231cfad80ca419 Mon Sep 17 00:00:00 2001
From: HcySunYang <HcySunYang@outlook.com>
Date: Fri, 31 Aug 2018 14:42:49 +0800
Subject: [PATCH 1/4] fix(#8728): only execute the dependArray function once

---
 src/core/observer/index.js                  |  3 ++-
 src/core/observer/watcher.js                |  7 ++++++
 test/unit/modules/observer/observer.spec.js | 27 +++++++++++++++++++++
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/core/observer/index.js b/src/core/observer/index.js
index 35469aaf16a..4770e88a8df 100644
--- a/src/core/observer/index.js
+++ b/src/core/observer/index.js
@@ -161,8 +161,9 @@ export function defineReactive (
       if (Dep.target) {
         dep.depend()
         if (childOb) {
+          const needDepend = Array.isArray(value) && !Dep.target.checkRelated(childOb.dep)
           childOb.dep.depend()
-          if (Array.isArray(value)) {
+          if (needDepend) {
             dependArray(value)
           }
         }
diff --git a/src/core/observer/watcher.js b/src/core/observer/watcher.js
index 725480d9215..a0715f99405 100644
--- a/src/core/observer/watcher.js
+++ b/src/core/observer/watcher.js
@@ -139,6 +139,13 @@ export default class Watcher {
     }
   }
 
+  /**
+   * Check if a dependency has been associated with the current watcher.
+   */
+  checkRelated (dep: Dep) {
+    return this.newDepIds.has(dep.id)
+  }
+
   /**
    * Clean up for dependency collection.
    */
diff --git a/test/unit/modules/observer/observer.spec.js b/test/unit/modules/observer/observer.spec.js
index 5f075bccc95..db1c6e48cc6 100644
--- a/test/unit/modules/observer/observer.spec.js
+++ b/test/unit/modules/observer/observer.spec.js
@@ -356,6 +356,33 @@ describe('Observer', () => {
     })
   })
 
+  it('Array\'s getter is triggered multiple times, the Watcher should only associate with Dep once.', () => {
+    const data = {
+      arr: [{}]
+    }
+    observe(data)
+    // mock a watcher!
+    const watcher = {
+      newDepIds: new Set(),
+      addDep (dep) {
+        this.newDepIds.add(dep.id)
+        dep.addSub(this)
+      },
+      checkRelated: function (dep) {
+        return this.newDepIds.has(dep.id)
+      }
+    }
+    spyOn(watcher, 'checkRelated').and.callThrough()
+    Dep.target = watcher
+    data.arr
+    data.arr
+    Dep.target = null
+    expect(watcher.checkRelated.calls.count()).toBe(2)
+    const allCalls = watcher.checkRelated.calls.all()
+    expect(allCalls[0].returnValue).toBe(false)
+    expect(allCalls[1].returnValue).toBe(true)
+  })
+
   it('warn set/delete on non valid values', () => {
     try {
       setProp(null, 'foo', 1)

From 956e535fe57ec5a788d0005b5ea9074cf9e4cc88 Mon Sep 17 00:00:00 2001
From: HcySunYang <HcySunYang@outlook.com>
Date: Fri, 31 Aug 2018 15:22:31 +0800
Subject: [PATCH 2/4] fix(flow): method call error

---
 src/core/observer/index.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/core/observer/index.js b/src/core/observer/index.js
index 4770e88a8df..44b686e6aea 100644
--- a/src/core/observer/index.js
+++ b/src/core/observer/index.js
@@ -158,10 +158,11 @@ export function defineReactive (
     configurable: true,
     get: function reactiveGetter () {
       const value = getter ? getter.call(obj) : val
-      if (Dep.target) {
+      const targetWatcher = Dep.target
+      if (targetWatcher) {
         dep.depend()
         if (childOb) {
-          const needDepend = Array.isArray(value) && !Dep.target.checkRelated(childOb.dep)
+          const needDepend = Array.isArray(value) && !targetWatcher.checkRelated(childOb.dep)
           childOb.dep.depend()
           if (needDepend) {
             dependArray(value)

From bfe76e0ee3ead720c161ab9bb2df9616670a9eeb Mon Sep 17 00:00:00 2001
From: HcySunYang <HcySunYang@outlook.com>
Date: Fri, 31 Aug 2018 15:51:37 +0800
Subject: [PATCH 3/4] fix(test): use polyfill Set

---
 test/unit/modules/observer/observer.spec.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/unit/modules/observer/observer.spec.js b/test/unit/modules/observer/observer.spec.js
index db1c6e48cc6..79cc5097c30 100644
--- a/test/unit/modules/observer/observer.spec.js
+++ b/test/unit/modules/observer/observer.spec.js
@@ -6,7 +6,7 @@ import {
   del as delProp
 } from 'core/observer/index'
 import Dep from 'core/observer/dep'
-import { hasOwn } from 'core/util/index'
+import { hasOwn, Set } from 'core/util/index'
 
 describe('Observer', () => {
   it('create on non-observables', () => {

From 62c232cdbac6d7d25f6fd5d1672eb33064eed18c Mon Sep 17 00:00:00 2001
From: HcySunYang <HcySunYang@outlook.com>
Date: Fri, 31 Aug 2018 15:57:36 +0800
Subject: [PATCH 4/4] fix(test): alias

---
 test/unit/modules/observer/observer.spec.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/unit/modules/observer/observer.spec.js b/test/unit/modules/observer/observer.spec.js
index 79cc5097c30..81d2008df33 100644
--- a/test/unit/modules/observer/observer.spec.js
+++ b/test/unit/modules/observer/observer.spec.js
@@ -6,7 +6,7 @@ import {
   del as delProp
 } from 'core/observer/index'
 import Dep from 'core/observer/dep'
-import { hasOwn, Set } from 'core/util/index'
+import { hasOwn, _Set as Set } from 'core/util/index'
 
 describe('Observer', () => {
   it('create on non-observables', () => {