Vue3中的watch用法

1. 监听对象

watch(age, (newVal, oldVal) => { console.log('age变了', newVal, oldVal) })
    watch(stu, (newVal, oldVal) => {
      console.log('stu变了', newVal, oldVal)
    }, { immediate: false, deep: false })

2. 监听数组， 两个一起监听，有一个变化，就执行

watch([age, stu], () => { console.log('有一个变了') })

3. 监听函数的返回值

watch(() => stu.address,
      (newVal, oldVal) => { console.log('stu.address', newVal, oldVal) },
      { immediate: false, deep: true }
    )