Optional dependencies

Optional dependencies in Angular are really powerful when you use or configure a dependency that may or may not exist or that has been provided within an Angular application. In this recipe, we'll learn how to use the @Optional decorator to configure optional dependencies in our components/services. We'll work with LoggerService and ensure our components do not break if it has not already been provided.

Getting ready

The project for this recipe resides in chapter03/start_here/ng-optional-dependencies. Perform the following steps:

1. Open the project in Visual Studio Code.
2. Open the Terminal, and run npm install to install the dependencies of the project.
3. Once done, run ng serve -o.

   This should open the app in a new browser tab. You should see something similar to the following screenshot:

Figure 3.2 – The ng-optional-dependencies app running on http://localhost:4200

Now that we have the app running...