Asynchronous providers

When the application start has to be delayed until some asynchronous tasks will be finished, for example, until the connection with the database will be established, you should consider using asynchronous providers. In order to create an async provider, we use the useFactory. The factory has to return a Promise (thus async functions fit as well).

{
  provide: 'AsyncDbConnection',
  useFactory: async () => {
    const connection = await createConnection(options);
    return connection;
  },
},

Hint Learn more about the custom providers syntax here.

Injection

The asynchronous providers can be simply injected to other components by their tokens (in the above case, by the AsyncDbConnection token). Each class that depends on the asynchronous provider will be instantiated once the async provider is already resolved.

The above example is for demonstration purposes. If you're looking for more detailed one, see here.