Using the event bus in external TypeScript projects

Using the event bus in external TypeScript projects is slightly difficult as TypeScript does not know of the type for the global variable eventBus. Additionally, using the interface functions will make the tests fail as the global is not defined.

Solving the first issue is relatively straight forward as we need to declare the variable so TypeScript knows of it. First install the package @keneanung/nexus-event-bus (i.e. through a terminal):

npm install @keneanung/nexus-event-bus

Then add the following to the top of the src/index.ts file:

import { IEventBus } from "@keneanung/nexus-event-bus";

declare global {
  // eslint-disable-next-line no-var
  var eventBus: IEventBus
};

The eslint-disable-next-line is there to prevent the ESLint rule no-var from complaining about the global variable. But we need to declare it as var to be able to assign it in tests.

To make the tests work, the easiest way would be to install the npm package jest-mock-extended as a development dependency and use it like this:

import { mock } from 'jest-mock-extended';
import { IEventBus } from '@keneanung/nexus-event-bus';

globalThis.eventBus = mock<IEventBus>();

test('My Greeter', () => {
  expect(Greeter('Carl')).toBe('');
});