Better types for wrapper.vm when the component is closed

[cexbrayat]

Since 2.0.0-rc.15, we are now exposing $.proxy as wrapper.vm to simplify testing of script setup component,
allowing to test the following component:

<script setup lang="ts">
import { ref } from 'vue'
const count = ref(0)
</script>

with expect(wrapper.vm.count).toBe(0), even if count is not exposed by the component (see PR #931 ).

This works, but for TS (vue-tsc), wrapper.vm does not have a count property, because wrapper.vm is typed as ComponentPublicInstance.

Ideally, we would like wrapper.vm type to reflect that it is actually not the component public instance, but the properties exposed to the template. Is there a way to infer that?

To reproduce, remove "exclude": ["tests/expose.spec.ts"] from tsconfig.volar.json, and run yarn vue-tsc. It fails with:

tests/expose.spec.ts:38:23 - error TS2339: Property 'count' does not exist on type '{ $: ComponentInternalInstance; $data: {}; $props: Partial<{}> & Omit<Readonly<{} & {} & {}> & VNodeProps & AllowedComponentProps & ComponentCustomProps, never>; ... 10 more ...; $watch(source: string | Function, cb: Function, options?: WatchOptions<...> | undefined): WatchStopHandle; } & ... 4 more ... & ComponentC...'.

38     expect(wrapper.vm.count).toBe(1)

For readers interested in this issue, you can workaround it with an explicit cast:
expect((wrapper.vm as unknown as { count: number }).count).toBe(1)

[cexbrayat]

@pikax do you have an idea how we could solve that?

[pikax]

Currently that's not possible, I'm working on this PR vuejs/core#4465 to improve some types, I can have a look on how to also add that info there

[cexbrayat]

For anyone keeping up with this, @johnsoncodehk released [email protected] with a new option that improves the situation. See #1170

[felixzapata]

The explicit cast solution stops working with the last Vue release (3.2.45).

[cexbrayat]

@felixzapata are you using VTU v2.2.2 ? There was a breaking change in Vue v3.2.45, but the latest VTU release should work around it.

[felixzapata]

sorry, I forgot to mention that with VTU 2.2.2 also fails. I mean, I tested with Vue 3.2.45 and VTU 2.2.2

[cexbrayat]

@felixzapata In that case, can you open an issue with a small repro using https://stackblitz.com/edit/vitest-dev-vitest-a961ap?file=package.json&initialPath=__vitest__ please? We'll take a look

[felixzapata]

I will try because, besides the standard packages, we have some custom configurations and TypeScript typing rules.

I am reviewing the tests that are failing; all the ones we have using casting in order to spy methods.

[felixzapata]

Is there a way to allow this mocking? Is similar to this one but the problem I think is because of mount and because I am late setting the mock. I think it should be during the mounting process.

[cexbrayat]

@felixzapata It is not possible, as this is not possible in vanilla JS. See #1798 (comment) for more explanation.

[felixzapata]

@felixzapata It is not possible, as this is not possible in vanilla JS. See #1798 (comment) for more explanation.

ok, maybe I have some thoughts of something similar I did in the past regarding the framework/library.

[matthew-dean]

This may have been improved for vue-tsc, but it still fails with Volar AFAIK.

[pm0u]

Is there any related issues for vue or volar that we could chime in on since this is an external issue?

[cexbrayat]

@pm0u I don't think there are such issues upstream (but maybe there are, I haven't checked recently).
@pikax was working on a PR to improve the situation if I remember correctly, but I'm not sure of its status

[pm0u]

I saw that, however it looks like that has been untouched since 9/2021. The TS version referenced in the package json is a major version behind, so probably safe to say it is stale

[ulfgebhardt]

In component:

const slide = ref(0)

defineExpose({ slide })

In test:

it('has slide value 0', () => {
  expect(wrapper.vm.slide).toBe(0)
})

Not sure if proper solution, but solves the typing without any casts.

[cexbrayat]

@ulfgebhardt Thanks, but your solution is expected to work: this issue is for the cases where you don't want to expose the variable.

[pikax]

This will require a few changes from https://github.com/vuejs/language-tools, since the SFC types are generated by it, I recommend creating a cross issue over there.