Effect for side effects in Angular - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when this Angular effect runs?

Consider this Angular effect that listens for a login action and triggers a side effect:

readonly loginEffect = this.effect<string>((login$) => {
  return login$.pipe(
    tap(username => console.log(`User logged in: ${username}`))
  );
});

What is the main behavior of this effect?

Angular

readonly loginEffect = this.effect<string>((login$) => {
  return login$.pipe(
    tap(username => console.log(`User logged in: ${username}`))
  );
});

A It modifies the username before passing it to the next effect in the chain.

B It dispatches a new action with the username after logging it to the console.

C It logs the username to the console whenever a login action occurs, without dispatching a new action.

D It cancels the login action and prevents further processing.

💡 Hint

Think about what tap does in RxJS streams.

The tap operator is used for side effects like logging. This effect listens to the login stream and logs the username but does not dispatch any new actions.

❓ state_output

intermediate

What is the output of this effect when triggered?

Given this Angular effect that triggers a notification service on a save action:

readonly saveEffect = this.effect((save$) => {
  return save$.pipe(
    tap(() => this.notificationService.show('Saved successfully'))
  );
});

What will happen when saveEffect runs?

Angular

readonly saveEffect = this.effect((save$) => {
  return save$.pipe(
    tap(() => this.notificationService.show('Saved successfully'))
  );
});

A The notification service will display 'Saved successfully' each time the save action occurs, without dispatching new actions.

B The effect will dispatch a new action with the notification message.

C Nothing happens because the effect does not subscribe to the save$ stream.

D The effect will cause a runtime error because it returns no observable.

💡 Hint

Remember that effects automatically subscribe to the observable returned.

The effect uses tap to call the notification service for side effects. Effects automatically subscribe, so the notification shows on each save.

📝 Syntax

advanced

Which option correctly defines an effect for side effects only?

Choose the correct Angular effect syntax that performs a side effect without dispatching a new action.

A readonly logEffect = this.effect((actions$) => actions$.pipe(tap(action => console.log(action))));

B readonly logEffect = this.effect((actions$) => actions$.pipe(map(action => ({ type: 'LOG', payload: action }))));

C readonly logEffect = this.effect((actions$) => actions$.pipe(filter(action => action.type === 'LOG')));

D readonly logEffect = this.effect((actions$) => actions$.pipe(reduce((acc, curr) => acc + 1, 0)));

💡 Hint

Look for the operator that performs side effects without changing the stream.

Option A uses tap which performs side effects without emitting new actions. Other options transform or filter the stream, which may dispatch actions or change behavior.

🔧 Debug

advanced

Why does this effect not trigger the side effect?

Look at this Angular effect:

readonly effectWithoutReturn = this.effect((actions$) => {
  actions$.pipe(
    tap(() => console.log('Effect triggered'))
  );
});

Why does the console log never appear when the effect runs?

Angular

readonly effectWithoutReturn = this.effect((actions$) => {
  actions$.pipe(
    tap(() => console.log('Effect triggered'))
  );
});

A Because console.log is asynchronous and does not run inside effects.

B Because the effect function does not return the observable, so it is never subscribed to.

C Because the effect should use map instead of tap to trigger side effects.

D Because the tap operator is used incorrectly and does not cause side effects.

💡 Hint

Check if the observable is returned from the effect function.

Effects must return an observable to be subscribed to. Without returning, the pipe is created but never executed, so side effects do not run.

🧠 Conceptual

expert

What is the key difference between effects for side effects and effects that dispatch actions?

In Angular, effects can either perform side effects only or dispatch new actions. What is the main difference in how these effects are defined and behave?

A Effects for side effects automatically unsubscribe, but dispatching effects never unsubscribe.

B Effects for side effects use the map operator, while effects that dispatch actions use tap.

C Effects for side effects must be declared in the component, while dispatching effects are declared in services.

D Effects for side effects return an observable that completes without emitting actions, while effects that dispatch actions emit new actions to the store.

💡 Hint

Think about what the effect returns and what the store expects.

Side effect-only effects return observables that do not emit actions, often using tap. Effects that dispatch actions emit new actions to the store, usually using map or similar operators.