NgRx store concept in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the NgRx StoreModule in an Angular standalone component.

Angular

import { StoreModule } from '@ngrx/store';

@Component({
  standalone: true,
  imports: [StoreModule.[1]({})],
  selector: 'app-root',
  template: `<h1>Welcome</h1>`
})
export class AppComponent {}

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

AforFeature

BcreateStore

CprovideStore

DforRoot

Attempts:

3 left

💡 Hint

Common Mistakes

Using forFeature instead of forRoot in the root component.

Trying to use createStore which is not a StoreModule method.

The StoreModule.forRoot method sets up the root store in an Angular app.

2fill in blank

medium

Complete the code to select a piece of state from the store using a selector.

Angular

this.userName$ = this.store.select([1]);

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

AfetchUserName

BgetUserName

CselectUserName

DloadUserName

Attempts:

3 left

💡 Hint

Common Mistakes

Using verbs like get or fetch which are not typical selector names.

Trying to call the selector instead of passing it as a reference.

Selectors are functions that extract slices of state. The common naming is selectUserName.

3fill in blank

hard

Fix the error in dispatching an action to the store.

Angular

this.store.[1](loadItems());

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

Atrigger

Bdispatch

Csend

Demit

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like emit or send.

Confusing dispatch with select.

The correct method to send actions to the store is dispatch.

4fill in blank

hard

Fill both blanks to define a reducer function with initial state and action handling.

Angular

export const counterReducer = createReducer(
  [1],
  on(increment, state => ({ count: state.count [2] 1 }))
);

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

A{ count: 0 }

B+

C-

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number instead of an object for initial state.

Using subtraction instead of addition for increment.

The initial state is an object with count 0, and the increment adds 1 to count.

5fill in blank

hard

Fill all three blanks to create a feature store module with a reducer and selector.

Angular

StoreModule.[1]('counter', [2]),

export const selectCounter = createFeatureSelector<CounterState>('[3]');

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

AforFeature

BcounterReducer

Ccounter

DforRoot

Attempts:

3 left

💡 Hint

Common Mistakes

Using forRoot instead of forFeature for feature modules.

Mismatching feature names in selector and module.

forFeature registers a feature store slice named 'counter' with its reducer. The selector uses the same feature name.

Practice

1. What is the primary purpose of the NgRx Store in an Angular application?

easy

A. To style components with CSS dynamically

B. To handle HTTP requests and responses automatically

C. To keep all application data in one central place for easy access and updates

D. To manage routing between different pages

Solution

1. Step 1: Understand NgRx Store role

   The NgRx Store is designed to hold the application state in one place.

2. Step 2: Compare with other options

   Options B, C, and D describe other Angular features, not the store's purpose.

3. Final Answer:

   To keep all application data in one central place for easy access and updates -> Option C

4. Quick Check:

   NgRx Store = Central app data storage [OK]

Hint: NgRx Store = single source of truth for app data [OK]

Common Mistakes:

• Confusing store with routing or HTTP services
• Thinking store manages styles or UI directly

2. Which of the following is the correct way to dispatch an action named loadItems using NgRx Store in a component?

easy

A. this.store.call(loadItems);

B. this.store.emit(loadItems);

C. store.dispatch = loadItems();

D. this.store.dispatch(loadItems());

Solution

1. Step 1: Recall NgRx dispatch syntax

   Actions are dispatched by calling this.store.dispatch(action()).

2. Step 2: Check other options for syntax errors

   Options A, B, and C use incorrect methods or assignment instead of dispatch call.

3. Final Answer:

   this.store.dispatch(loadItems()); -> Option D

4. Quick Check:

   Dispatch action = this.store.dispatch(action()) [OK]

Hint: Dispatch actions with this.store.dispatch(action()) [OK]

Common Mistakes:

• Using emit or call instead of dispatch
• Assigning dispatch instead of calling it

3. Given this reducer snippet:

const initialState = { count: 0 };
function counterReducer(state = initialState, action) {
  switch(action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    default:
      return state;
  }
}

What will be the state after dispatching { type: 'increment' } twice starting from initial state?

medium

A. { count: 0 }

B. { count: 2 }

C. { count: 1 }

D. { count: -2 }

Solution

1. Step 1: Analyze reducer behavior for 'increment'

   Each 'increment' action adds 1 to the current count.

2. Step 2: Apply two increments starting from 0

   0 + 1 = 1 after first increment, then 1 + 1 = 2 after second increment.

3. Final Answer:

   { count: 2 } -> Option B

4. Quick Check:

   Two increments = count 2 [OK]

Hint: Add 1 per 'increment' action to count [OK]

Common Mistakes:

• Counting only one increment
• Confusing decrement with increment

4. Identify the error in this NgRx reducer code:

function todoReducer(state = [], action) {
  if (action.type === 'add') {
    state.push(action.payload);
    return state;
  }
  return state;
}

medium

A. Mutating state directly instead of returning a new state

B. Missing default case in reducer

C. Incorrect action type string

D. Reducer should not return state

Solution

1. Step 1: Check state mutation

   The reducer uses state.push(), which changes the original array directly.

2. Step 2: Understand NgRx immutability rule

   Reducers must return new state objects without mutating the old state.

3. Final Answer:

   Mutating state directly instead of returning a new state -> Option A

4. Quick Check:

   Reducers must be pure and immutable [OK]

Hint: Never mutate state; always return new object/array [OK]

Common Mistakes:

• Using push instead of spread operator
• Ignoring immutability in reducers

5. You want to create a feature state slice for user profiles using NgRx. Which combination correctly sets up the feature state and selector?

1. Define interface UserProfileState { name: string; age: number; }
2. Create reducer userProfileReducer
3. Register feature state with key 'userProfile'
4. Select user name from store

Which code snippet correctly selects the user name?

hard

A. const selectUserProfile = createFeatureSelector<UserProfileState>('userProfile');
const selectUserName = createSelector(selectUserProfile, state => state.name);

B. const selectUserName = createSelector('userProfile', state => state.name);

C. const selectUserProfile = createSelector('userProfile');
const selectUserName = state => state.name;

D. const selectUserName = createFeatureSelector<UserProfileState>('userProfile').pipe(map(state => state.name));

Solution

1. Step 1: Understand feature selector usage

   Use createFeatureSelector with the feature key to get the feature state.

2. Step 2: Create selector for user name

   Use createSelector with the feature selector and a projector function to select the name.

3. Final Answer:

   const selectUserProfile = createFeatureSelector<UserProfileState>('userProfile'); const selectUserName = createSelector(selectUserProfile, state => state.name); -> Option A

4. Quick Check:

   Feature selector + createSelector = correct pattern [OK]

Hint: Use createFeatureSelector then createSelector for nested state [OK]

Common Mistakes:

• Passing string directly to createSelector
• Using pipe on selector instead of RxJS operators in component