Property does not exist on the type in vue-class-component

I created new vue with typescript application using latest @vue/cli (v3). When I use component decorator from vue-class-component with computed/props/methods, I got an error:

Property 'count' does not exist on type 'HelloWorld'.Vetur(2339)

Here my code:

<script lang="ts">
import { Prop, Vue } from "vue-property-decorator";

import Component from "vue-class-component";

@Component({
  computed: {
    count() {
      return 'blabla';
    }
  }
})
export default class HelloWorld extends Vue {
  @Prop() private msg!: string;

  onClick() {
    const y = this.count;
  }
}
</script>

But according to the example it should be working fine. How do I fix this?

[ReinisV]

From the first example on the landing page

You need to write that getter differently.

Unfortunately, decorators (as they are proposed/implemented now) cannot modify the type that they decorate, which is why nothing you ever pass to the decorator will ever show up in a typesafe manner.

And the example that you mention has a workaround added for this specific issue

[ktsn]

This is because decorator cannot change the class instance type. You have to declare the property type by yourself or use some decorator like vuex-class to map getters on class properties.