Property does not exist on the type in vue-class-component
The documentation you linked states:
Following is the example written in Babel. If you are looking for TypeScript version, it's in the example directory.
Example:
<script lang="ts"> import Vue from 'vue'; import { Component } from 'vue-class-component'; const AppProps = Vue.extend({ props: { propMessage: String } }) @Component export default class YourComponent extends AppProps { get something() { return this.propMessage; } }</script>