深入理解vue.js中$watch的oldvalue与newValue

data: {
 arr: [{
  name: '笨笨',
  address: '上海'
 }, {
  name: '笨笨熊',
  address: '北京'
 }],
 obj: {
  name: '呆呆',
  address: '苏州'
 },
 str: '哈哈哈'
 }

watch: {
 arr: function(newValue, oldValue) {
  console.log(newValue, oldValue)
  console.log(JSON.stringify(oldValue) === JSON.stringify(newValue))
 },
 obj: function(newValue, oldValue) {
  console.log(newValue, oldValue)
  console.log(JSON.stringify(oldValue) === JSON.stringify(newValue))
 },
 str: function(newValue, oldValue) {
  console.log(newValue, oldValue)
  console.log(JSON.stringify(oldValue) === JSON.stringify(newValue))
 },
 }

methods: {
 test() {
  this.arr.push({
  name: 9
  })
  this.$set(this.obj, 'i', 0)
  this.str = ''
 },
 test1() {
  this.arr = [{
  name: '000'
  }]
  this.obj = {
  name: 999
  }
  this.str = '123'
 }
 }

arr = [...arr]

obj = {...obj}