RouterModule configuration in Angular - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of RouterModule.forRoot() in Angular?

It sets up the main routes for the Angular application and configures the router at the app's root level. It should be called once in the root module.

beginner

How do you define a route path and its associated component in Angular's RouterModule?

You create an object with a path string and a component reference, then include it in the routes array passed to RouterModule.forRoot() or RouterModule.forChild().

intermediate

What is the difference between RouterModule.forRoot() and RouterModule.forChild()?

forRoot() configures the router at the app root and should be used once. forChild() is for feature modules to add routes without reconfiguring the root router.

intermediate

How can you enable scrolling to top on route change using RouterModule configuration?

By passing an extra option { scrollPositionRestoration: 'top' } to RouterModule.forRoot(routes, { scrollPositionRestoration: 'top' }).

intermediate

What does the useHash option do in RouterModule configuration?

Setting useHash: true makes Angular use hash-based URLs (like example.com/#/path) which can help with older server setups that don't support HTML5 pushState.

Which method is used to configure the root routes in Angular?

A RouterModule.forChild()

B RouterModule.configure()

C RouterModule.forRoot()

D RouterModule.setup()

RouterModule.forRoot() is used once to set up the main routes of the app.

How do you add routes in a feature module without affecting the root router?

A RouterModule.forChild()

B RouterModule.extend()

C RouterModule.addRoutes()

D RouterModule.forRoot()

RouterModule.forChild() adds routes in feature modules safely.

What option enables scrolling to the top when navigating to a new route?

A scrollPositionRestoration: 'top'

B scrollPositionRestoration: 'enabled'

C scrollToTop: true

D scrollPositionRestoration: 'auto'

Use scrollPositionRestoration: 'top' to scroll to top on route change.

What does setting useHash: true do in RouterModule configuration?

A Prevents route guards

B Disables routing

C Enables lazy loading

D Enables hash-based URLs

It enables hash-based URLs like example.com/#/path.

Where should RouterModule.forRoot() be called?

A In every feature module

B Only in the root app module

C In service files

D In component files

It should be called only once in the root app module.

Explain how to configure routes in Angular using RouterModule.

Think about how you tell Angular which component to show for each URL.

Describe the purpose and usage of the useHash option in RouterModule configuration.

Consider how URLs look and how servers handle them.

Practice

1. What is the main purpose of RouterModule.forRoot(routes) in an Angular app?

easy

A. To create a new Angular component

B. To configure the app's routes and enable navigation based on URL paths

C. To style the app's components

D. To fetch data from a server

Solution

1. Step 1: Understand RouterModule role

   RouterModule is used to manage navigation and views based on URL paths in Angular.

2. Step 2: Role of forRoot method

   The forRoot method sets up the routes for the whole app, telling Angular which component to show for each path.

3. Final Answer:

   To configure the app's routes and enable navigation based on URL paths -> Option B

4. Quick Check:

   RouterModule.forRoot sets routes [OK]

Hint: Remember: forRoot sets main routes once per app [OK]

Common Mistakes:

• Confusing forRoot with creating components
• Thinking RouterModule styles components
• Assuming it fetches data

2. Which of the following is the correct syntax to import RouterModule with routes in an Angular module?

easy

A. RouterModule(routes)

B. imports: RouterModule.forRoot(routes)

C. imports: [RouterModule.forRoot(routes)]

D. RouterModule.import(routes)

Solution

1. Step 1: Check Angular module imports syntax

   Angular modules expect an array for the imports property.

2. Step 2: Correct use of RouterModule.forRoot

   RouterModule.forRoot(routes) returns a module configured with routes and must be inside an array.

3. Final Answer:

   imports: [RouterModule.forRoot(routes)] -> Option C

4. Quick Check:

   Imports must be an array with forRoot call [OK]

Hint: Always wrap RouterModule.forRoot in an array for imports [OK]

Common Mistakes:

• Omitting the array brackets in imports
• Using RouterModule.import which doesn't exist
• Calling RouterModule as a function directly

3. Given this route configuration:

const routes = [
  { path: '', component: HomeComponent },
  { path: 'about', component: AboutComponent }
];

What component will Angular display when the URL path is /about?

medium

A. AboutComponent

B. HomeComponent

C. No component, shows error

D. Both HomeComponent and AboutComponent

Solution

1. Step 1: Match URL path to route

   The URL path '/about' matches the route with path 'about'.

2. Step 2: Identify component for matched route

   The route with path 'about' uses AboutComponent.

3. Final Answer:

   AboutComponent -> Option A

4. Quick Check:

   Path '/about' shows AboutComponent [OK]

Hint: Match URL path exactly to route path to find component [OK]

Common Mistakes:

• Assuming empty path '' matches '/about'
• Thinking multiple components show at once
• Expecting error for valid path

4. Identify the error in this RouterModule configuration:

const routes = [
  { path: 'home', component: HomeComponent },
  { path: 'profile' component: ProfileComponent }
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule {}

medium

A. Routes array should be inside imports array

B. RouterModule.forRoot should be RouterModule.forChild

C. AppRoutingModule should not export RouterModule

D. Missing comma between 'profile' path and component property

Solution

1. Step 1: Check routes array syntax

   Between 'path: 'profile'' and 'component: ProfileComponent' a comma is missing, causing syntax error.

2. Step 2: Verify RouterModule usage and exports

   Using RouterModule.forRoot(routes) and exporting RouterModule is correct here.

3. Final Answer:

   Missing comma between 'profile' path and component property -> Option D

4. Quick Check:

   Comma missing in object properties causes error [OK]

Hint: Check commas between object properties in routes [OK]

Common Mistakes:

• Confusing forRoot and forChild usage
• Placing routes array incorrectly
• Removing exports of RouterModule

5. You want to add a default route that redirects empty path '' to '/home' using RouterModule. Which configuration is correct?

hard

A. { path: '', redirectTo: '/home', pathMatch: 'full' }

B. { path: '', redirectTo: 'home' }

C. { path: '', component: HomeComponent, redirectTo: '/home' }

D. { redirectTo: '/home', path: '', pathMatch: 'prefix' }

Solution

1. Step 1: Understand redirectTo usage

   To redirect from '' path, use redirectTo with full path and specify pathMatch as 'full' to match exact empty path.

2. Step 2: Check options for correct syntax

   { path: '', redirectTo: '/home', pathMatch: 'full' } correctly uses redirectTo with '/home' and pathMatch: 'full'. { path: '', redirectTo: 'home' } misses pathMatch, C wrongly combines component and redirectTo, D uses 'prefix' which causes partial matching issues.

3. Final Answer:

   { path: '', redirectTo: '/home', pathMatch: 'full' } -> Option A

4. Quick Check:

   Redirect empty path with pathMatch 'full' [OK]

Hint: Use pathMatch: 'full' when redirecting empty path [OK]

Common Mistakes:

• Omitting pathMatch property
• Combining component with redirectTo
• Using pathMatch: 'prefix' for empty path redirect