Revert "simplify array change detection"

This reverts commit 5590378.

Author: yyx990803

Diff for: src/runtime/observer/patch-array.js renamed to src/runtime/observer/array.js

@@ -1,18 +1,32 @@
-import { def, toArray } from '../util/index'
+import { def } from '../util/index'
 
 const arrayProto = Array.prototype
-const mutationMethods = ['push', 'pop', 'shift', 'unshift', 'splice', 'sort', 'reverse']
+export const arrayMethods = Object.create(arrayProto)
 
 /**
- * Intercept mutating methods and notify change
+ * Intercept mutating methods and emit events
  */
 
-mutationMethods.forEach(function (method) {
+;[
+  'push',
+  'pop',
+  'shift',
+  'unshift',
+  'splice',
+  'sort',
+  'reverse'
+]
+.forEach(function (method) {
   // cache original method
   var original = arrayProto[method]
-
-  var interceptor = function arrayMutationInterceptor () {
-    var args = toArray(arguments)
+  def(arrayMethods, method, function mutator () {
+    // avoid leaking arguments:
+    // http://jsperf.com/closure-with-arguments
+    var i = arguments.length
+    var args = new Array(i)
+    while (i--) {
+      args[i] = arguments[i]
+    }
     var result = original.apply(this, args)
     var ob = this.__ob__
     var inserted
@@ -31,12 +45,7 @@ mutationMethods.forEach(function (method) {
     // notify change
     ob.dep.notify()
     return result
-  }
-
-  arrayProto[method] = function () {
-    let fn = this && this.__ob__ ? interceptor : original
-    return fn.apply(this, arguments)
-  }
+  })
 })
 
 /**

Diff for: src/runtime/observer/index.js

@@ -1,13 +1,16 @@
-import './patch-array'
 import Dep from './dep'
+import { arrayMethods } from './array'
 import {
   def,
   isArray,
   isObject,
   isPlainObject,
+  hasProto,
   hasOwn
 } from '../util/index'
 
+const arrayKeys = Object.getOwnPropertyNames(arrayMethods)
+
 /**
  * By default, when a reactive property is set, the new value is
  * also converted to become reactive. However in certain cases, e.g.
@@ -40,6 +43,10 @@ export function Observer (value) {
   this.dep = new Dep()
   def(value, '__ob__', this)
   if (isArray(value)) {
+    var augment = hasProto
+      ? protoAugment
+      : copyAugment
+    augment(value, arrayMethods, arrayKeys)
     this.observeArray(value)
   } else {
     this.walk(value)
@@ -111,6 +118,37 @@ Observer.prototype.removeVm = function (vm) {
   this.vms.$remove(vm)
 }
 
+// helpers
+
+/**
+ * Augment an target Object or Array by intercepting
+ * the prototype chain using __proto__
+ *
+ * @param {Object|Array} target
+ * @param {Object} src
+ */
+
+function protoAugment (target, src) {
+  /* eslint-disable no-proto */
+  target.__proto__ = src
+  /* eslint-enable no-proto */
+}
+
+/**
+ * Augment an target Object or Array by defining
+ * hidden properties.
+ *
+ * @param {Object|Array} target
+ * @param {Object} proto
+ */
+
+function copyAugment (target, src, keys) {
+  for (var i = 0, l = keys.length; i < l; i++) {
+    var key = keys[i]
+    def(target, key, src[key])
+  }
+}
+
 /**
  * Attempt to create an observer instance for a value,
  * returns the new observer if successfully observed,

Diff for: src/runtime/util/env.js

@@ -1,5 +1,8 @@
 /* global MutationObserver */
 
+// can we use __proto__?
+export const hasProto = '__proto__' in {}
+
 // Browser environment sniffing
 export const inBrowser =
   typeof window !== 'undefined' &&