vue3中的watch和computed怎么使用

<template>
  <p>{{ age }}</p>
  <button @click="age++">click</button>
</template>

<script>
  import { watch, ref } from 'Vue'
  export default {
      name: 'App',
      setup() {
          const age = ref(18)
          // 监听 ref 数据 age，会触发后面的回调，不需要 .value
          watch(age, (newValue, oldValue) => {
              console.log(newValue, oldValue)
          })

          return { age }
      },
  }
</script>

<template>
    <p>age: {{ age }} num: {{ num }}</p>
    <button @click="handleClick">click</button>
</template>

<script>
    import { watch, ref } from 'vue'
    export default {
        name: 'App',
        setup() {
            const age = ref(18)
            const num = ref(0)

            const handleClick = () => {
                age.value++
                num.value++
            }
            // 数组里面是 ref 数据
            watch([age, num], (newValue, oldValue) => {
                console.log(newValue, oldValue)
            })

            return { age, num, handleClick }
        },
    }
</script>

                {
                    immediate: true,
                }

<template>
    <p>{{ age }}</p>
    <button @click="handleClick">click</button>
</template>

<script>
    import { watch, ref } from 'vue'
    export default {
        name: 'App',
        setup() {
            const age = ref(18)

            const handleClick = () => {
                age.value++
            }

            watch(
                age,
                (newValue, oldValue) => {
                    console.log(newValue, oldValue) // 18 undefined
                },
                {
                    immediate: true,
                }
            )

            return { age, handleClick }
        },
    }
</script>

? 问题：修改 ref 对象里面的数据并不会触发监听，说明 ref 并不是默认开启 deep 的。见下

<template>
    <p>{{ obj.hobby.eat }}</p>
    <button @click="obj.hobby.eat = '面条'">修改 obj.hobby.eat</button>
</template>

<script>
    import { watch, ref } from 'vue'
    export default {
        name: 'App',
        setup() {
            const obj = ref({
                hobby: {
                    eat: '西瓜',
                },
            })
            // 注意：ref 监听对象，默认监听的是这个对象地址的变化
            watch(obj, (newValue, oldValue) => {
                console.log(newValue === oldValue)
            })

            return { obj }
        },
    }
</script>

watch(
    obj,
    (newValue, oldValue) => {
        console.log(newValue, oldValue)
        console.log(newValue === oldValue)
    },
    {
        deep: true,
    }
)

<template>
    <p>{{ obj.hobby.eat }}</p>
    <button @click="obj.hobby.eat = '面条'">修改 obj</button>
</template>

<script>
    import { watch, ref } from 'vue'
    export default {
        name: 'App',
        setup() {
            const obj = ref({
                hobby: {
                    eat: '西瓜',
                },
            })
            watch(obj.value, (newValue, oldValue) => {
                console.log(newValue, oldValue)
                console.log(newValue === oldValue)
            })

            return { obj }
        },
    }
</script>

<template>
    <p>{{ obj.hobby.eat }}</p>
    <button @click="obj.hobby.eat = '面条'">修改 obj</button>
</template>

<script>
    import { watch, reactive } from 'vue'
    export default {
        name: 'App',
        setup() {
            const obj = reactive({
                hobby: {
                    eat: '西瓜',
                },
            })
            // 把 obj.hobby 作为普通值去进行监听，只能监听到 obj.hobby 自身的变化
            
            // 如果开启了深度监听，则能监听到 obj.hobby 和内部数据的所有变化
            
            // 能监听影响到 obj.hobby.eat 变化的操作，例如 obj.hobby = { eat: '面条' } 或 obj.hobby.eat = '面条'，如果是 reactive 直接对 obj 的修改则不会被监听到（ref 可以）
            watch(
                () => obj.hobby.eat,
                (newValue, oldValue) => {
                    console.log(newValue, oldValue)
                    console.log(newValue === oldValue)
                }
            )
            return { obj }
        },
    }
</script>

<template>
  <p>firstName: {{ person.firstName }}</p>
  <p>lastName: {{ person.lastName }}</p>
  <input type="text" v-model="person.fullName" />
</template>
<script>
  import { computed, reactive } from 'vue'
  export default {
      name: 'App',
      setup() {
          const person = reactive({
              firstName: '初',
              lastName: '映',
          })
          // 也可以传入对象，目前和上面等价
          person.fullName = computed({
              get() {
                  return person.firstName + '*' + person.lastName
              },
              set(value) {
                console.log(value,'value');//为上述get的返回值
                  const newArr = value.split('*')
                  person.firstName = newArr[0]
                  person.lastName = newArr[1]
              },
          })
          return {
              person,
          }
      },
  }
</script>