Usage and best practice guide for watch in Vue3

watch(WatcherSource, Callback, [WatchOptions])

type WatcherSource<T> = Ref<T> | (() => T)

interface WatchOptions extends WatchEffectOptions {
    deep?: boolean // default: false
  immediate?: boolean // default: false
  
}

<template>
  <div class="watch-test">
    <div>name：{{name}}</div>
    <div>age:{{age}}</div>
  </div>
  <div>
    <button @click="changeName">Change Name</button>
    <button @click="changeAge">Change age</button>
  </div>
</template>

<script>
  import {ref, watch} from 'vue'

  export default {
    name: 'Home',
    setup() {

      const name = ref('小松楠奈')
      const age = ref(25)

      const watchFunc = watch([name, age], ([name, age], [prevName, prevAge]) => {
        console.log('newName', name, 'oldName', prevName)
        console.log('newAge', age, 'oldAge', prevAge)
        if (age > 26) {
          watchFunc() // Stop monitoring}
      },{immediate:true})

      const changeName = () => {
        name.value = 'Arimura Kasumi'
      }
      const changeAge = () => {
        age.value += 2
      }
      return {
        name,
        age,
        changeName,
        changeAge
      }
    }
  }
</script>

<template>
  <div class="watch-test">
    <div>ref defines an array: {{arrayRef}}</div>
    <div>reactive definition array: {{arrayReactive}}</div>
  </div>
  <div>
    <button @click="changeArrayRef">Change the first item of the ref definition array</button>
    <button @click="changeArrayReactive">Change the first item of the reactive definition array</button>
  </div>
</template>

<script>
  import {ref, reactive, watch} from 'vue'

  export default {
    name: 'WatchTest',
    setup() {
      const arrayRef = ref([1, 2, 3, 4])
      const arrayReactive = reactive([1, 2, 3, 4])

      //ref not deep
      const arrayRefWatch = watch(arrayRef, (newValue, oldValue) => {
        console.log('newArrayRefWatch', newValue, 'oldArrayRefWatch', oldValue)
      })

      //ref deep
      const arrayRefDeepWatch = watch(arrayRef, (newValue, oldValue) => {
        console.log('newArrayRefDeepWatch', newValue, 'oldArrayRefDeepWatch', oldValue)
      }, {deep: true})

      //reactive, source is not a function const arrayReactiveWatch = watch(arrayReactive, (newValue, oldValue) => {
        console.log('newArrayReactiveWatch', newValue, 'oldArrayReactiveWatch', oldValue)
      })

      // Best Practices for Array Watching - reactive and source returns in a functional way, returning copied data const arrayReactiveFuncWatch = watch(() => [...arrayReactive], (newValue, oldValue) => {
        console.log('newArrayReactiveFuncWatch', newValue, 'oldArrayReactiveFuncWatch', oldValue)
      })

      const changeArrayRef = () => {
        arrayRef.value[0] = 6
      }
      const changeArrayReactive = () => {
        arrayReactive[0] = 6
      }
      return {
        arrayRef,
        arrayReactive,
        changeArrayRef,
        changeArrayReactive
      }
    }
  }
</script>

<template>
  <div class="watch-test">
    <div>user:{</div>
      <div>name:{{objReactive.user.name}}</div>
      <div>age:{{objReactive.user.age}}</div>
    <div>}</div>
    <div>brand:{{objReactive.brand}}</div>
    <div>
      <button @click="changeAge">Change age</button>
    </div>
  </div>
</template>

<script>
  import {ref, reactive, watch} from 'vue'
  import _ from 'lodash';

  export default {
    name: 'WatchTest',
    setup() {
      const objReactive = reactive({user: {name: '小松菜奈', age: '20'}, brand: 'Channel'})

      //reactive source is a function const objReactiveWatch = watch(() => objReactive, (newValue, oldValue) => {
        console.log('objReactiveWatch')
        console.log('new:',JSON.stringify(newValue))
        console.log('old:',JSON.stringify(oldValue))
      })

      //reactive, source is function, deep: true
      const objReactiveDeepWatch = watch(() => objReactive, (newValue, oldValue) => {
        console.log('objReactiveDeepWatch')
        console.log('new:',JSON.stringify(newValue))
        console.log('old:',JSON.stringify(oldValue))
      }, {deep: true})

      // Best Practices for Object Deep Watching - reactive and source returns in a functional way, returning deep-copied data const objReactiveCloneDeepWatch = watch(() => _.cloneDeep(objReactive), (newValue, oldValue) => {
        console.log('objReactiveCloneDeepWatch')
        console.log('new:',JSON.stringify(newValue))
        console.log('old:',JSON.stringify(oldValue))
      })

      const changeAge = () => {
        objReactive.user.age = 26
      }

      return {
        objReactive,
        changeAge
      }
    }
  }
</script>