Type error with Option API

[sxzz]

<template>
  <div></div>
</template>

<script lang="ts">
import { defineComponent } from 'vue';

export default defineComponent({
  data() {
    return {
      a: {
        b: '',
      },
    };
  },
  computed: {
    length() {
      return this.a.b;
      /**
       * 类型“CreateComponentPublicInstance<{} | {}, {}, {}, {}, {}, ComponentOptionsMixin, ComponentOptionsMixin, EmitsOptions, {} | {}, {}, false, ... 6 more ..., {}>”上不存在属性“a”。
  类型“{ $: ComponentInternalInstance; $data: {}; $props: {} | {}; $attrs: Data; $refs: Data; $slots: Readonly<InternalSlots>; ... 7 more ...; $watch(source: string | Function, cb: Function, options?: WatchOptions<...> | undefined): WatchStopHandle; } & ... 4 more ... & ComponentCustomProperties”上不存在属性“a”。ts(2339)
       */
    },
  },
});
</script>

src/test.vue:18:19 - error TS2339: Property 'a' does not exist on type 'CreateComponentPublicInstance<{} | {}, {}, {}, {}, {}, ComponentOptionsMixin, ComponentOptionsMixin, EmitsOptions, {} | {}, {}, false, ... 6 more ..., {}>'.
  Property 'a' does not exist on type '{ $: ComponentInternalInstance; $data: {}; $props: {} | {}; $attrs: Data; $refs: Data; $slots: Readonly<InternalSlots>; ... 7 more ...; $watch(source: string | Function, cb: Function, options?: WatchOptions<...> | undefined): WatchStopHandle; } & ... 4 more ... & ComponentCustomProperties'.

18       return this.a.b;
                     ~

[johnsoncodehk]

This is correct report, you can reproduce this error in *.ts file with same code.

Vue Land TS discord server may help.

[sxzz]

Thanks.

Solution: vuejs/vue#8721 (comment)