Effect for side effects in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an effect that logs a message when an action is dispatched.

Angular

readonly logEffect = createEffect(() => this.actions$.pipe(tap(() => console.log([1]))));

Drag options to blanks, or click blank then click option'

Adispatch

Bthis.actions$

C'Action dispatched!'

Dconsole.log

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a function instead of a string to console.log

Trying to dispatch an action inside tap

The tap operator is used here to perform a side effect: logging a message. The message string should be passed inside console.log.

2fill in blank

medium

Complete the code to create a non-dispatching effect that shows an alert when the 'loginSuccess' action occurs.

Angular

readonly alertEffect = createEffect(() => this.actions$.pipe(ofType('loginSuccess'), tap(() => alert([1]))), { dispatch: [2] });

Drag options to blanks, or click blank then click option'

Afalse

B'Login successful!'

Ctrue

D'Error occurred!'

Attempts:

3 left

💡 Hint

Common Mistakes

Setting dispatch to true when no action is dispatched

Passing a boolean instead of a string to alert

The alert function shows a message. The message should be a string like 'Login successful!'. The dispatch option should be set to false to indicate no new action is dispatched.

3fill in blank

hard

Fix the error in the effect that should log the action type but currently does not work.

Angular

readonly logActionType = createEffect(() => this.actions$.pipe(tap(action => console.log(action.[1]))));

Drag options to blanks, or click blank then click option'

Atype

Bname

Cpayload

Devent

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name' or 'payload' which are not standard action properties

Trying to log the whole action object instead of a property

Actions have a type property that describes the action name. Logging action.type shows which action was dispatched.

4fill in blank

hard

Fill both blanks to create an effect that listens for 'logout' action and navigates to the login page without dispatching a new action.

Angular

readonly logoutEffect = createEffect(() => this.actions$.pipe(ofType([1]), tap(() => this.router.[2]('/login'))), { dispatch: false });

Drag options to blanks, or click blank then click option'

A'logout'

B'login'

Cnavigate

DnavigateByUrl

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'login' instead of 'logout' in ofType

Using router.navigate with an array instead of navigateByUrl with a string

The effect listens for the 'logout' action. To navigate programmatically, router.navigateByUrl is used to go to the '/login' page. The effect does not dispatch a new action.

5fill in blank

hard

Fill all three blanks to create an effect that listens for 'loadData' action, calls a service method, and logs the result without dispatching a new action.

Angular

readonly loadDataEffect = createEffect(() => this.actions$.pipe(ofType([1]), switchMap(() => this.dataService.[2]().pipe(tap(result => console.log([3]))))), { dispatch: false });

Drag options to blanks, or click blank then click option'

A'loadData'

BfetchData

Cresult

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong action name or service method

Logging an undefined variable inside tap

The effect listens for the 'loadData' action. It calls the service method fetchData which returns an observable. The result is logged inside tap using the variable result. The effect does not dispatch a new action.

Practice

1. What is the main purpose of an Effect in Angular?

easy

A. To style components with CSS dynamically

B. To define the main UI layout of a component

C. To handle user input events directly in the template

D. To run side tasks like data loading or logging when app state changes

Solution

1. Step 1: Understand what side effects mean in Angular

   Side effects are extra tasks like fetching data or logging that happen outside the main app logic.

2. Step 2: Identify the role of Effects

   Effects run these side tasks automatically when app state changes, keeping main logic clean.

3. Final Answer:

   To run side tasks like data loading or logging when app state changes -> Option D

4. Quick Check:

   Effect = side tasks on state change [OK]

Hint: Effects run extra tasks when app data changes [OK]

Common Mistakes:

• Thinking Effects handle UI layout
• Confusing Effects with event handlers
• Believing Effects style components

2. Which of the following is the correct way to create an Effect in Angular using RxJS operators?

easy

A. createEffect(() => this.actions$.subscribe(action => console.log(action)))

B. createEffect(() => this.actions$.map(action => action.type))

C. createEffect(() => this.actions$.pipe(ofType(loadData), tap(() => console.log('Loading'))))

D. createEffect(() => this.actions$.filter(action => action.type === 'loadData'))

Solution

1. Step 1: Recall the correct RxJS operators for Effects

   Effects use pipe with operators like ofType to filter actions and tap for side effects.

2. Step 2: Check each option's syntax

   createEffect(() => this.actions$.pipe(ofType(loadData), tap(() => console.log('Loading')))) correctly uses pipe, ofType, and tap. Others misuse operators or subscribe directly, which is incorrect inside Effects.

3. Final Answer:

   createEffect(() => this.actions$.pipe(ofType(loadData), tap(() => console.log('Loading')))) -> Option C

4. Quick Check:

   Effect uses pipe + ofType + tap [OK]

Hint: Use pipe with ofType and tap inside createEffect [OK]

Common Mistakes:

• Using subscribe inside createEffect
• Using map instead of tap for side effects
• Using filter without ofType

3. Given this Effect code snippet:

loadData$ = createEffect(() => this.actions$.pipe(
  ofType('LOAD_DATA'),
  tap(() => console.log('Data loading started'))
), { dispatch: false });

What will happen when the 'LOAD_DATA' action is dispatched?

medium

A. The message 'Data loading started' is logged, and no new action is dispatched

B. The message is logged and a new action is dispatched automatically

C. Nothing happens because dispatch is false

D. An error occurs because tap cannot be used here

Solution

1. Step 1: Understand the effect's dispatch option

   Setting dispatch: false means this Effect does not send out new actions after running.

2. Step 2: Analyze the tap operator

   The tap operator runs side code like logging but does not change or dispatch actions.

3. Final Answer:

   The message 'Data loading started' is logged, and no new action is dispatched -> Option A

4. Quick Check:

   dispatch false means no new action, tap logs side effect [OK]

Hint: dispatch: false means no new action dispatched [OK]

Common Mistakes:

• Assuming tap dispatches actions
• Thinking dispatch: false disables effect
• Confusing tap with map or switchMap

4. Identify the error in this Effect code:

saveData$ = createEffect(() => this.actions$.pipe(
  ofType('SAVE_DATA'),
  map(() => this.api.save()),
  tap(() => console.log('Save triggered'))
));

medium

A. Using map without returning an action causes an error

B. tap cannot be used after map

C. ofType should be replaced with filter

D. createEffect must not use arrow functions

Solution

1. Step 1: Check the map operator usage

   map must return a new action object for dispatching, but this.api.save() likely returns a Promise or void, not an action.

2. Step 2: Understand effect dispatch requirements

   Effects expect actions to be returned for dispatch unless dispatch: false is set, which is missing here.

3. Final Answer:

   Using map without returning an action causes an error -> Option A

4. Quick Check:

   map must return action for dispatch [OK]

Hint: map must return an action unless dispatch: false [OK]

Common Mistakes:

• Ignoring missing action return in map
• Thinking tap cannot follow map
• Confusing ofType with filter

5. You want to create an Effect that listens for a 'LOGIN' action, calls an async login API, and then dispatches either 'LOGIN_SUCCESS' or 'LOGIN_FAILURE' based on the result. Which code snippet correctly implements this?

hard

A. login$ = createEffect(() => this.actions$.pipe(
ofType('LOGIN'),
tap(() => this.authService.login()),
map(() => ({ type: 'LOGIN_SUCCESS' }))
));

B. login$ = createEffect(() => this.actions$.pipe(
ofType('LOGIN'),
switchMap(action => this.authService.login(action.credentials).pipe(
map(user => ({ type: 'LOGIN_SUCCESS', user })),
catchError(() => of({ type: 'LOGIN_FAILURE' }))
))
));

C. login$ = createEffect(() => this.actions$.pipe(
filter(action => action.type === 'LOGIN'),
map(() => this.authService.login()),
map(user => ({ type: 'LOGIN_SUCCESS', user }))
));

D. login$ = createEffect(() => this.actions$.pipe(
ofType('LOGIN'),
map(action => this.authService.login(action.credentials)),
map(user => ({ type: 'LOGIN_SUCCESS', user }))
));

Solution

1. Step 1: Identify async handling with switchMap

   Using switchMap allows calling the async login API and switching to its result stream.

2. Step 2: Handle success and error properly

   Inside switchMap, map creates a success action, and catchError returns a failure action wrapped in of to keep the stream alive.

3. Final Answer:

   login$ = createEffect(() => this.actions$.pipe( ofType('LOGIN'), switchMap(action => this.authService.login(action.credentials).pipe( map(user => ({ type: 'LOGIN_SUCCESS', user })), catchError(() => of({ type: 'LOGIN_FAILURE' })) )) )); -> Option B

4. Quick Check:

   Use switchMap + map + catchError for async effects [OK]

Hint: Use switchMap with map and catchError for async API calls [OK]

Common Mistakes:

• Using tap instead of switchMap for async calls
• Not handling errors with catchError
• Returning promises instead of observables