What is a DI token?

A DI token is a lookup token associated with a dependency provider in dependency injection system. The injector maintains an internal token-provider map that it references when asked for a dependency and the DI token is the key to the map. Let's take example of DI Token usage,

const BASE_URL = new InjectionToken() < string > 'BaseUrl';
const injector = Injector.create({
  providers: [{ provide: BASE_URL, useValue: 'http://some-domain.com' }],
});
const url = injector.get(BASE_URL);