Typesafety in Vue3 Store pattern

I am using the Vue3 Store pattern as described here. https://vuejs.org/guide/scaling-up/state-management.html#simple-state-management-with-reactivity-api

My store However is a Typescript file, as I would like to add type safety to my store.

I can't really find how to add that...

import {reactive} from "vue";

export const ColorService = reactive({
    loading: false,

    toggleLoading(): void {
        this.loading = !this.loading;
    }
});

How can I add type safety for loading to make sure it is a boolean?