vue + typescript：Property 'xxx' does not exist on type 'Vue'.

related codes and errors:
 

export default Vue.extend({

  props: {

    menu: {

      type: Array,

      default: () => []

    }

  },

  name: 'navHeaderMenu',

  data() {

    return {

      hoverIndex: ''

    }

  },

  methods: {

    triggerToMousemove(i: number): void {

      // if I used this method：

      // vscode would shows：Property 'hoverIndex' does not exist on type 'Vue'.

      this.houverIndex = i

      // vscode error：Property 'test' does not exist no type 'Vue'.

      this.ab()

      // if I wrote like these：

      // vscode no errors

      (this as any).houverIndex = i

      (this as any).test()

      this.$emit('mouseover', i)

    },

    triggerToMouseout(i: number): void {

      (this as any).hoverIndex = ''

      this.$emit('mouseout', i)

    },

    test() {

        console.log('test')

    },

  },

})

 
how to fix this error:Property xxx does not exist on type 'Vue'