1-2 @Watch

<template>
  <div id="app">
     <input type="text" v-model="msg">
  </div>
</template>
<script lang="ts">
import { Vue,Component,Watch } from "vue-property-decorator";
@Component({})
export default class App extends Vue {
  private msg:string = "hello world"
  @Watch("msg")
  onMsg(val:string):void{
    console.log(val)
  }
}
</script>