[Vue + Typescript] Property does not exist on type in computed function

Version

2.5.17

Reproduction link

https://codesandbox.io/s/10l5yrl9rq

Steps to reproduce

Codesandbox seems not support typescript code intelligense in *.vue, the file is src/index.vue

Here is the code:

<script lang="ts">
import Vue from 'vue'

interface TestInterface {
  a: string
}

export default Vue.extend({
  props: {
    prop1: {
      type: Object as () => TestInterface,
    },
  },
  computed: {
    computed1() {
      return this.prop1.a
    }
  }
})
</script>

What is expected?

Typescript compiler will not complaint

What is actually happening?

Property ‘prop1’ does not exist on type ‘{ computed1(): any; }’.

Is there any way to solve this problem?

[stayacid]

Let me left a note for everyone who’re confused as i am: annotate ALL return types of computed properties.

[ktsn]

Please read https://vuejs.org/v2/guide/typescript.html You should do the following things to make type inference works.

• set strict: true or noImplicitThis: true for compiler option.
• annotate return type of computed properties.