Inject stuff even outside components scope

app-inject.ts

import { App, InjectionKey } from 'vue';

/**
 * Inject a service using Vue app reference and the injection key.
 * Use this to inject a service when outside a component scope (eg. into a Quasar boot file),
 * where Vue `inject` won't work.
 * This is expecially useful when the data is provided from a third-party package
 * which only expose the injection key.
 *
 * @example
 * // src/boot/books.ts
 * import { boot } from 'quasar/wrappers';
 * import { BooksServiceInjectionKey } from 'book-manager';
 *
 * export default boot(({ app }) => {
 *   const booksService = appInject(app, BooksServiceInjectionKey);
 *   // ... business ah-ah ...
 * })
 */
export function appInject<T>(app: App, injectionKey: InjectionKey<T>) {
  return app._context.provides[
    // Needs explicit casting to symbol, see: https://github.com/microsoft/TypeScript/issues/46956
    // TODO: should be solved by https://github.com/vuejs/vue-next/pull/5089
    injectionKey as symbol
  ] as T;
}