# Property Type Declaration

Sometimes, you have to define component properties and methods out of a class component. For example, Vuex, the official state management library for Vue, provides mapGetters and mapActions helpers to map a store to component properties and methods. These helpers need to be used in a component options object.

Even in this case, you can pass component options to the @Component decorator's argument. However it does not automatically declare the properties and methods on type level while they work on runtime.

You need to manually declare their types in the class component:

import Vue from 'vue'
import Component from 'vue-class-component'
import { mapGetters, mapActions } from 'vuex'

// Interface of post
import { Post } from './post'

  computed: mapGetters([

  methods: mapActions([
export default class Posts extends Vue {
  // Declare mapped getters and actions on type level.
  // You may need to add `!` after the property name
  // to avoid compilation error (definite assignment assertion).

  // Type the mapped posts getter.
  posts!: Post[]

  // Type the mapped fetchPosts action.
  fetchPosts!: () => Promise<void>

  mounted() {
    // Use the mapped getter and action.
    this.fetchPosts().then(() => {