provide any channel to watch props change in directive

<div v-custom-dir="{ a }"></div>

app.directive("custom-dir", {
  // support `props` 
  props: ["a"],
  // add `props` arguments when mounted or provide setup hook
  mounted(props) {
     // watch props change
     watch(() => props.a, console.log)
  }
})

l know using component can resolve it，but l need to modify DOM，it will append an extra node，and change it's behavior when props was changed

now l depend on update hook，it will emit when parent updated

app.directive("custom-dir", {
   update(el, { value }){
     if(value.a === "b"){
         // do something
       }
  }
})

Is there any other way?