Vue-typescript-component not working reactivity?

Question

JavaScript

Why doesn't the template change when the method is used?

<template>
  {{count}}
</template>

When I do this, the change occurs in the template

export default{
 data():Object{
   return {
     count: 0
   }
 },
  methods: {
     plus():void{
        this.count++
     }
 }
}

And through the Vue-typescript-componen classes, changes in the template do not work

export default class Aaa extends Vue{


     count :number= 0


     plus():void{
        this.count++
     }
}