Service-based state management in Angular - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is service-based state management in Angular?

It is a way to keep and share data across components using Angular services. Services hold the state and provide methods to update or get data, so components stay in sync.

beginner

Why use a service for state management instead of component properties?

Services allow multiple components to access and update the same data easily. Component properties are local and isolated, so sharing state between components is harder without services.

intermediate

How do Angular services keep state persistent across components?

Angular services are singletons by default when provided in root. This means one instance is shared across the app, so the state inside the service stays consistent and accessible.

intermediate

What Angular feature helps components react to state changes in a service?

Using RxJS Observables inside services lets components subscribe to state changes. When the service updates data, subscribers get notified and update their views automatically.

beginner

Show a simple example of a service holding a counter state with increment method.

import { Injectable } from '@angular/core';

@Injectable({ providedIn: 'root' })
export class CounterService {
  private count = 0;

  getCount() { return this.count; }

  increment() { this.count++; }
}

This service keeps count and lets components get or increase it.

What is the main benefit of using a service for state management in Angular?

A Sharing state easily across multiple components

B Making components heavier

C Avoiding use of RxJS

D Keeping state only inside one component

Services allow multiple components to share and update the same state easily.

How does Angular ensure a service is a singleton by default?

A By importing it multiple times

B By creating a new instance for each component

C By using component decorators

D By providing it in the root injector

Providing a service in root makes Angular create one shared instance for the whole app.

Which RxJS feature is commonly used in services to notify components about state changes?

A Observable

B Promise

C Callback

D EventEmitter

Observables let components subscribe and react to changes in service state.

What happens if you store state only in a component property?

A State is saved in a database

B State is shared automatically

C State is local and not shared with other components

D State is lost when component reloads

Component properties are local to that component and not shared.

Which Angular decorator is used to make a class a service?

A @Component()

B @Injectable()

C @NgModule()

D @Directive()

@Injectable() marks a class as a service that can be injected.

Explain how service-based state management works in Angular and why it is useful.

Think about how one place can keep data for many parts of your app.

Describe how you can notify Angular components about changes in service state.

Consider how a message system can tell others when data changes.