What Is Injectors?
A service is just a class in Angular until you register with an Angular dependency injector.
The injector is responsible for creating angular service instances and injecting them into classes.
You rarely create an injector yourself and Angular creates automatically during the bootstrap process.
Angular doesn't know automatically how you want to create instances of your services or injector. You must configure it by specifying providers for every service. Actually, providers tell the injector how to create the service and without a provider not able to create the service.
Bootstrap defines the components that should be bootstrapped when this module is bootstrapped. The components listed here will automatically be added to entryComponents.
Explore in detail by using below questions -
2. What Are @Injectable providers?
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