Type errors using properties with Vue3 SFC with TypeScript

Question

I'm quite stuck trying to use properties with Vue3. I've tried a few different approaches, but all of them fail the type-check phase (e.g.: yarn build).

My project is a brand new vue3-ts project created using Vite. This is my component:

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

export default defineComponent({
  name: "Test",
  props: {
    label: {
      type: String as PropType<string>,
      required: true,
    },
  },
  methods:  {
    onClick() {
      console.log(this.label);  // This line yields an error!
    },
  },
});
</script>

I get an error that this.label does not exist: Property 'label' does not exist on type 'CreateComponentPublicInstance<Readonly<ExtractPropTypes<Readonly<ComponentPropsOptions<Data>>>> & ...

(volar complains about the same thing).

I've tried a few different approaches with no better luck, these are:

---

Using the <script setup> approach defining props:

<script setup lang="ts">
const props = defineProps({
  classes: String,
  label: String,
})
</script>

This also warns about the unused props variable. That's not a big deal, but the above error is still there.

---

Using a setup method on my component:

  setup(props) {

    defineProps({
      classes: String,
      label: String,
    })
  },

---

Using the old-school form of defining props, a bit overzealous with defining types:

export default defineComponent({
  name: "AppStory",
  props: {
    label: {
      type: String as PropType<string>,
      required: true,
    },
  },

---

A slightly less zealous approach with the types:

export default defineComponent({
  name: "AppStory",
  props: {
    label: {
      type: String,
      required: true,
    },
  },

---

Does anyone have a working example of SFC with Vue3 that use properties? What am I doing wrong? All the examples I'm finding out there have no props, or don't use TS. Vue'3 docs aren't very TS-centric, and no examples seem to cover this (rather basic) scenario.

Answer 1

well I created a new vite application using the vue-ts setup by default, and the only thing you're missing in the first example is the import of the. PropType type.

<template>
  <div>
    <button @click="onClick">{{ label }}</button>
  </div>
</template>
<script lang="ts">
import { defineComponent, PropType } from "vue";

export default defineComponent({
  name: "Test",
  props: {
    label: {
      type: String as PropType<string>,
      required: true,
    },
  },
  methods: {
    onClick() {
      console.log(this.label); // This line yields an error!
    },
  },
});
</script>

And this is the parent component (default App.vue component)

<script setup lang="ts">
// This starter template is using Vue 3 <script setup> SFCs
// Check out https://v3.vuejs.org/api/sfc-script-setup.html#sfc-script-setup
import HelloWorld from "./components/HelloWorld.vue";
</script>

<template>
  <img alt="Vue logo" src="./assets/logo.png" />
  <HelloWorld label="Hello Vue 3 + TypeScript + Vite" />
</template>

<style>
#app {
  font-family: Avenir, Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}
</style>

This is working fine for me.

Now the same example with the setup keyword in the script tag:

<template>
  <div>
    <button @click="onClick">{{ label }}</button>
  </div>
</template>

<script lang="ts" setup>
import { PropType } from "vue";
const props = defineProps({
  label: {
    type: String as PropType<string>,
    required: true,
  },
});

const onClick = () => {
  console.log(props.label); // This line yields an error!
};
</script>

It also works.

And finally using the setup method:

<template>
  <div>
    <button @click="onClick">{{ label }}</button>
  </div>
</template>

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

export default defineComponent({
  name: "Test",
  props: {
    label: {
      type: String as PropType<string>,
      required: true,
    },
  },
  setup(props) {
    const onClick = () => {
      console.log(props.label); // This line yields an error!
    };
    return { onClick };
  },
});
</script>

Hopefully, this will solve your issue.