Route guards (canActivate, canDeactivate) in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to implement a canActivate guard that allows navigation only if the user is logged in.

Angular

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): boolean {
  return this.authService.[1]();
}

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

AisLoggedIn

BcheckUser

CcanActivate

DallowAccess

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method that does not return a boolean

Calling a method that does not exist in authService

The isLoggedIn method checks if the user is logged in and returns a boolean. This is the correct method to use in a canActivate guard.

2fill in blank

medium

Complete the code to implement a canDeactivate guard that asks the user for confirmation before leaving the page.

Angular

canDeactivate(component: any, currentRoute: ActivatedRouteSnapshot, currentState: RouterStateSnapshot, nextState?: RouterStateSnapshot): boolean {
  return window.[1]('Do you really want to leave?');
}

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

Aprompt

BconfirmLeave

Calert

Dconfirm

Attempts:

3 left

💡 Hint

Common Mistakes

Using alert which does not return a value

Using prompt which returns a string, not a boolean

The window.confirm method shows a dialog box with OK and Cancel buttons and returns true if OK is clicked. This is suitable for canDeactivate guards.

3fill in blank

hard

Fix the error in the canActivate guard method to properly return an Observable<boolean>.

Angular

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<boolean> {
  return this.authService.isLoggedIn()[1](map(loggedIn => loggedIn));
}

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

A.map

B.subscribe

C.pipe

D.then

Attempts:

3 left

💡 Hint

Common Mistakes

Using subscribe which returns a Subscription, not an Observable

Using then which is for Promises, not Observables

In Angular with RxJS, pipe is used to chain operators on Observables. Using pipe with a map operator is the correct way to transform the Observable.

4fill in blank

hard

Fill both blanks to create a canDeactivate guard that calls a component method to check if it can deactivate.

Angular

canDeactivate(component: [1], currentRoute: ActivatedRouteSnapshot, currentState: RouterStateSnapshot, nextState?: RouterStateSnapshot): boolean {
  return component.[2]();
}

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

ACanComponentDeactivate

BcanDeactivate

CcanLeave

DconfirmExit

Attempts:

3 left

💡 Hint

Common Mistakes

Using a component type that does not define canDeactivate

Calling a method name that does not exist on the component

The guard expects the component to implement CanComponentDeactivate interface and call its canDeactivate method to decide if navigation is allowed.

5fill in blank

hard

Fill all three blanks to create a route configuration that uses both canActivate and canDeactivate guards.

Angular

const routes: Routes = [
  {
    path: 'edit',
    component: EditComponent,
    canActivate: [[1]],
    canDeactivate: [[2]],
    data: { title: '[3]' }
  }
];

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

AAuthGuard

BUnsavedChangesGuard

CEdit Page

DLoginGuard

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up canActivate and canDeactivate guards

Using guard names that do not exist in the project

The AuthGuard protects the route from unauthorized access (canActivate). The UnsavedChangesGuard prevents leaving the page with unsaved changes (canDeactivate). The data title is set to 'Edit Page' for display purposes.

Practice

1. What is the primary purpose of the canActivate guard in Angular routing?

easy

A. To handle errors during route navigation.

B. To check if navigation to a route is allowed before entering it.

C. To preload data before the route loads.

D. To confirm if navigation away from a route is allowed.

Solution

1. Step 1: Understand the role of canActivate

   canActivate is a route guard that runs before entering a route to decide if navigation is allowed.

2. Step 2: Differentiate from other guards

   canDeactivate checks leaving a route, not entering. Preloading and error handling are unrelated to canActivate.

3. Final Answer:

   To check if navigation to a route is allowed before entering it. -> Option B

4. Quick Check:

   canActivate = check before entering route [OK]

Hint: canActivate controls entering routes, canDeactivate controls leaving [OK]

Common Mistakes:

• Confusing canActivate with canDeactivate
• Thinking canActivate preloads data
• Assuming canActivate handles errors

2. Which of the following is the correct syntax to apply a canDeactivate guard to a route in Angular?

easy

A. { path: 'edit', component: EditComponent, canDeactivate: [UnsavedChangesGuard] }

B. { path: 'edit', component: EditComponent, canLoad: [LoadGuard] }

C. { path: 'edit', component: EditComponent, canActivate: [AuthGuard] }

D. { path: 'edit', component: EditComponent, canActivateChild: [ChildGuard] }

Solution

1. Step 1: Identify the guard type for leaving routes

   canDeactivate is used to check if navigation away from a route is allowed.

2. Step 2: Match syntax with canDeactivate

   The correct syntax uses canDeactivate: [GuardName] inside the route object.

3. Final Answer:

   { path: 'edit', component: EditComponent, canDeactivate: [UnsavedChangesGuard] } -> Option A

4. Quick Check:

   canDeactivate syntax = canDeactivate: [Guard] [OK]

Hint: Use canDeactivate: [Guard] to protect leaving a route [OK]

Common Mistakes:

• Using canActivate instead of canDeactivate for leaving routes
• Confusing canLoad with canDeactivate
• Missing brackets around guard name

3. Given this canDeactivate guard code snippet, what will happen when the user tries to leave the EditComponent with unsaved changes?

export class UnsavedChangesGuard implements CanDeactivate<EditComponent> {
  canDeactivate(component: EditComponent): boolean {
    if (component.hasUnsavedChanges()) {
      return confirm('You have unsaved changes. Leave anyway?');
    }
    return true;
  }
}

medium

A. The guard throws an error because confirm is not allowed.

B. The user is always allowed to leave without confirmation.

C. The user is blocked from leaving if there are unsaved changes.

D. The user is asked to confirm leaving only if there are unsaved changes.

Solution

1. Step 1: Analyze the guard logic

   The guard checks if component.hasUnsavedChanges() returns true, then asks for confirmation.

2. Step 2: Understand the confirm behavior

   If the user confirms, confirm() returns true allowing navigation; otherwise, navigation is blocked.

3. Final Answer:

   The user is asked to confirm leaving only if there are unsaved changes. -> Option D

4. Quick Check:

   canDeactivate confirms only if unsaved changes exist [OK]

Hint: canDeactivate can prompt user to confirm leaving [OK]

Common Mistakes:

• Assuming user can leave without confirmation always
• Thinking guard blocks leaving without prompt
• Believing confirm causes errors in Angular guards

4. Identify the error in this canActivate guard implementation:

export class AuthGuard implements CanActivate {
  canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot) {
    if (this.authService.isLoggedIn()) {
      return true;
    }
  }
}

medium

A. Missing return statement when user is not logged in.

B. Incorrect method name; should be canDeactivate.

C. The guard should return a Promise, not boolean.

D. The guard must not use services inside canActivate.

Solution

1. Step 1: Check all code paths return a value

   If isLoggedIn() is false, the method returns nothing (undefined), which is invalid.

2. Step 2: Understand guard return requirements

   canActivate must return true, false, or an observable/promise resolving to those. Missing return causes errors.

3. Final Answer:

   Missing return statement when user is not logged in. -> Option A

4. Quick Check:

   All canActivate paths must return true/false [OK]

Hint: Always return true or false in all canActivate paths [OK]

Common Mistakes:

• Not returning false or redirect when unauthorized
• Confusing canActivate with canDeactivate method names
• Thinking services can't be used in guards

5. You want to prevent users from leaving a form page if they have unsaved changes, but only if they are editing (not creating new). Which approach correctly uses canDeactivate to achieve this?

hard

A. Use canActivate guard to check unsaved changes before entering the form route.

B. Use canDeactivate guard that always returns true to allow navigation.

C. Use canDeactivate guard that checks component.isEditing and component.hasUnsavedChanges() before confirming navigation.

D. Use canActivateChild guard to block leaving the form.

Solution

1. Step 1: Identify when to block navigation away

   Blocking leaving only applies when editing and unsaved changes exist, so guard must check both conditions.

2. Step 2: Use canDeactivate guard properly

   canDeactivate runs when leaving a route, so it is the correct place to check and confirm navigation.

3. Final Answer:

   Use canDeactivate guard that checks component.isEditing and component.hasUnsavedChanges() before confirming navigation. -> Option C

4. Quick Check:

   canDeactivate with condition on editing and unsaved changes [OK]

Hint: Check editing and unsaved changes inside canDeactivate guard [OK]

Common Mistakes:

• Using canActivate to block leaving routes
• Always returning true in canDeactivate guard
• Confusing canActivateChild with canDeactivate