Defining routes array in Angular - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the routes array in Angular?

The routes array defines the paths and their corresponding components for navigation in an Angular app. It tells Angular which component to show when a user visits a specific URL.

beginner

How do you define a simple route for a HomeComponent with path 'home'?

You add an object like { path: 'home', component: HomeComponent } inside the routes array.

beginner

What does the empty string path ('') represent in the routes array?

It represents the default or root path of the app, usually shown when the user visits the base URL.

intermediate

How can you define a route that redirects from one path to another?

Use an object with path, redirectTo, and pathMatch properties, like { path: '', redirectTo: 'home', pathMatch: 'full' }.

intermediate

Why is the order of routes in the routes array important?

Angular matches routes in order. More specific routes should come before less specific ones to avoid incorrect matches.

What property in a route object specifies which component to display?

A path

B redirectTo

C component

D loadChildren

The 'component' property tells Angular which component to show for that route.

How do you define a route that redirects from '' to 'home'?

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

B { path: '', loadChildren: 'home.module' }

C { path: 'home', redirectTo: '' }

D { path: '', component: HomeComponent }

Redirect routes use 'redirectTo' and 'pathMatch' to specify the redirect behavior.

What does the 'pathMatch: "full"' option mean in a redirect route?

A Match the full URL path exactly

B Match any part of the URL

C Ignore the URL path

D Match only the first segment

'full' means the entire URL path must match for the redirect to happen.

Where should you place wildcard routes (like '**') in the routes array?

A In the middle

B At the end

C At the beginning

D Anywhere

Wildcard routes should be last because Angular checks routes in order.

Which Angular module uses the routes array to configure routing?

A BrowserModule

B HttpClientModule

C FormsModule

D RouterModule

RouterModule.forRoot(routes) sets up routing using the routes array.

Explain how to define a routes array in Angular and what each route object needs.

Think about how Angular knows which component to show for a URL.

Describe why the order of routes in the routes array matters and give an example.

Consider what happens if a wildcard route is first.

Practice

1. What does the routes array in Angular define?

easy

A. It defines the styles for each component.

B. It lists all services used in the app.

C. It tells Angular which component to show for each URL path.

D. It sets the database connection strings.

Solution

1. Step 1: Understand the purpose of routes array

   The routes array maps URL paths to components so Angular knows what to display.

2. Step 2: Eliminate unrelated options

   Styles, services, and database connections are not handled by routes.

3. Final Answer:

   It tells Angular which component to show for each URL path. -> Option C

4. Quick Check:

   Routes array = component mapping [OK]

Hint: Routes array links URL paths to components [OK]

Common Mistakes:

• Confusing routes with styles or services
• Thinking routes handle backend connections
• Assuming routes define component logic

2. Which of the following is the correct way to define a route for path 'home' with component HomeComponent?

easy

A. { path: 'home', component: HomeComponent }

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

C. { route: 'home', component: HomeComponent }

D. { path: 'home', component: 'HomeComponent' }

Solution

1. Step 1: Check correct property names

   The route object must have path and component properties.

2. Step 2: Verify component value type

   The component value should be the component class, not a string or redirect.

3. Final Answer:

   { path: 'home', component: HomeComponent } -> Option A

4. Quick Check:

   Use path and component keys correctly [OK]

Hint: Use component class, not string or redirectTo for components [OK]

Common Mistakes:

• Using 'route' instead of 'path'
• Setting component as a string
• Using redirectTo instead of component for components

3. Given this routes array:

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

What component will Angular show when the URL path is '/contact'?

medium

A. HomeComponent

B. AboutComponent

C. No component, error occurs

D. NotFoundComponent

Solution

1. Step 1: Match URL path to routes

   Path '/contact' does not match '' or 'about'.

2. Step 2: Use wildcard '**' route

   The '**' path catches all unmatched URLs and shows NotFoundComponent.

3. Final Answer:

   NotFoundComponent -> Option D

4. Quick Check:

   Wildcard '**' = NotFoundComponent [OK]

Hint: Unmatched paths go to '**' route component [OK]

Common Mistakes:

• Assuming empty path matches all URLs
• Thinking unmatched paths cause errors
• Confusing wildcard '**' with empty path

4. Identify the error in this routes array:

const routes = [
  { path: '', component: HomeComponent },
  { path: 'profile', redirectTo: 'user' },
  { path: 'user', component: UserComponent }
];

What is wrong with the route for 'profile'?

medium

A. redirectTo should be used with pathMatch property.

B. redirectTo cannot be used in routes array.

C. component is missing for 'profile' route.

D. Path 'user' should be capitalized.

Solution

1. Step 1: Check redirectTo usage

   When using redirectTo, Angular requires a pathMatch property to specify matching strategy.

2. Step 2: Confirm missing pathMatch causes error

   Without pathMatch, Angular cannot decide when to redirect, causing routing errors.

3. Final Answer:

   redirectTo should be used with pathMatch property. -> Option A

4. Quick Check:

   redirectTo needs pathMatch [OK]

Hint: Always add pathMatch with redirectTo routes [OK]

Common Mistakes:

• Omitting pathMatch with redirectTo
• Thinking redirectTo needs component
• Assuming path names must be capitalized

5. You want to define routes so that:
- The home page shows HomeComponent at path ''.
- The about page shows AboutComponent at path 'about'.
- Any unknown path redirects to home.

Which routes array correctly implements this?

hard

A. [
{ path: '', component: HomeComponent },
{ path: 'about', component: AboutComponent },
{ path: '**', redirectTo: '' }
]

B. [
{ path: '', component: HomeComponent },
{ path: 'about', component: AboutComponent },
{ path: '**', redirectTo: '', pathMatch: 'full' }
]

C. [
{ path: '', component: HomeComponent },
{ path: 'about', component: AboutComponent },
{ path: '*', redirectTo: '', pathMatch: 'full' }
]

D. [
{ path: '', component: HomeComponent },
{ path: 'about', component: AboutComponent },
{ path: '**', component: HomeComponent }
]

Solution

1. Step 1: Check wildcard path for unknown URLs

   The wildcard path for unknown URLs is '**', not '*'.

2. Step 2: Confirm redirectTo usage with pathMatch

   Redirect routes must include pathMatch: 'full' to work properly.

3. Step 3: Verify redirect target and components

   Redirecting '**' to '' sends unknown URLs to home page correctly.

4. Final Answer:

   [ { path: '', component: HomeComponent }, { path: 'about', component: AboutComponent }, { path: '**', redirectTo: '', pathMatch: 'full' } ] -> Option B

5. Quick Check:

   Use '**' with redirectTo and pathMatch 'full' [OK]

Hint: Use '**' wildcard with redirectTo and pathMatch 'full' [OK]

Common Mistakes:

• Using '*' instead of '**' for wildcard
• Omitting pathMatch in redirectTo routes
• Using component instead of redirectTo for redirects