How to use the watch listener for Vue2 and Vue3

 data（）{
     return{
         num:10
     }
 }，
 watch:{
      num:{
	      /*
	        * newValue: current value
            * oldValue: Modify the value of the previous moment
	        */
          handler(newValue,oldValue){
          	// doSomething
          }，
          /*
            * deep:Boolean: Deep monitoring
            * true: If the listening heap changes are
            * false: only listen for changes to the stack (default)
            */
          deep:true/false,
          /*
            * immediate:Boolean: Whether to execute handler function when the first definition is defined
            * true: Execute handler function when the first definition is
            * false: After modifying, execute the handler function
            */          
          immediate:true/false
      }      
  }

const num = ref(0)
1. Import  import {watch} from 'vue'
2. use
	 `const Return value= watch(Values ​​that need to be monitored, (newVal,oldVal)=>{ }, {deep,immediate,flush})`
	 
	 Return value: You can turn off the monitoring： Return value()
	 Parameter 1: Values ​​that need to be monitored
	 			 Basic data types(Number,String,Boolean,null,undefined)：  ()=>Basic data types值
	 			 Complex data types(Array,Object,Function)：			Write directly/()=>Basic data types值
	 Parameter 2: analogyVue2In-househandlerfunction
	 Parameter Three: {}Object, Object中可以有个配置项:deep,immediate,flush,
	 		deep,immediateThe meaning is described above, Here is the main oneflushExplanation of the value of:
	 			 `flush:post/sync/pre
      				   pre（default value）:Before rendering，The value has changed，No renderingdom
      				   post:After rendering，The value has changed，Also rendereddom
    				   sync:Change once rendering once，每一次都是Before rendering`