Watch monitors the data defined by ref
1.ref data basic data type
let sum=ref（0）
const stopWatch=watch（sum,(new,old)=>{
If(new>=10){
stopWatch()
}
console.log(‘sum数据变化了’)
}）
2. The ref data is an object type, and what is monitored is the address value of the object. If you want to monitor the changes in the internal attribute values of the object, you need to manually enable in-depth monitoring.
let person=ref（{
name：’张三’,age:22}）
watch（person,(new,old)=>{
console.log(‘person数据变化了’，new,old)//打印出来的new和old是一样的数据，因为地址没变
}，{
deep：true}）
3. Monitor the object type data defined by reactive, and in-depth monitoring is enabled by default
watch(person,(new,old)=>{ console.log('person data has changed', new, old)//The printed new and old are the same data, because the address has not changed })
4. Listen to a certain attribute in the reactive object, and the attribute is a basic data type and needs to be written in a functional form
watch（（）=>person.name,(new,old)=>{
console.log(‘person数据变化了’，new,old)//打印出来的new和old是不一样的
}）
//监听person.car 可以监听到changeC1、changeC2，但监听不到changeCar里的变化
watch（person.car,(new,old)=>{
console.log(‘person数据变化了’，new,old)//打印出来的new和old是不一样的
}）
//监听person.car写函数式，即监听地址 不能监听到changeC1、changeC2，但能监听到changeCar里的变化
watch（（）=>person.car,(new,old)=>{
console.log(‘person数据变化了’，new,old)}）
//监听person.car写函数式，加deep可以监听即监听changeC1、changeC2 也监听到changeCar里的变化
watch（（）=>person.car,(new,old)=>{
console.log(‘person数据变化了’，new,old)}，{
deep：true}）
Summary: What is monitored is the attributes in the object, so it is best to write functional expressions. Note: If the object monitors the address value, you need to pay attention to the inside of the object, and you need to manually enable in-depth monitoring.
5. Monitor multiple data array forms
watch（[()=>person.name,()=>person.car.c1],(new,old)=>{
console.log(‘person数据变化了’，new,old)
}）
watchEffect monitors data
watchEffect(()=>{
If(temp.value>=60||height.value>=80){
Console.log(‘已达标’)
}
})