Using globalProperties in Vue 3 and Typescript

Question

I've added a global property in main.ts, and am trying to access this in a component. however I'm getting the error:

Property '$const' does not exist on type 'ComponentPublicInstance<{}, {}, {}, {}, {}, EmitsOptions, {}, {}, false, ComponentOptionsBase<{}, {}, {}, {}, {}, ComponentOptionsMixin, ComponentOptionsMixin, EmitsOptions, string, {}>>'.Vetur(2339)

I think I need to augment the type, typescript considers $const to be any type right now, however I don't know how to do this in Vue 3 and there is no mention in the docs.

main.ts

import { createApp } from "vue";
import App from "./App.vue";
import store from "./store";
import * as constants from "@constants";

const app = createApp(App);

app.config.globalProperties.$const = Object.freeze(constants);

app.use(store);

app.mount("#app");

component

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

export default defineComponent({
  name: "Header",

  computed: {
    tags() {
      return Object.entries(this.$const.TAGS);
    }
  }
});
</script>

Any help would be appreciated.

Answer 1

You can augment the @vue/runtime-core TypeScript module in your application:

declare module '@vue/runtime-core' {
  interface ComponentCustomProperties {
    $const: Record<string, unknown>;
  }
}

export {}  // Important! See note.

Here is a documentation: ComponentCustomProperties

Important note: TS module augmentation works correctly only when it is placed in a module.

In TypeScript, just as in ECMAScript 2015, any file containing a top-level import or export is considered a module. Conversely, a file without any top-level import or export declarations is treated as a script whose contents are available in the global scope (and therefore to modules as well).

Therefore the file must contain at least one top-level import or export statement, even if empty one (as in the example above) - Type Augmentation Placement