Angular Interview Questions and Answers - Part 21
Angular is a popular single-page application design framework and development platform. It is a robust open-source JavaScript framework that is widely used for front-end application development. Nowadays Angular is very common as frontend technology so it is very common for the interview point as well.
Introduction
This is the Angular Interview Questions and Answers series. Here we will see 200+ Most Frequently Asked Angular Interview Questions. This is the 21st part of the Angular Interview Questions and Answer series.
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In this part we will discuss the following Important Angular Interview Questions:
Q235. What are the wildcard routes in Angular? Why it is important in any application?
Q236. What are URL Redirects in Angular? How can you set up redirects in the Angular?
Q237. What is the pathMatch in Angular? What is the default value of the pathMatch?
Q238. What is the difference between pathMatch and redirectTo in Angular?
Q239. What is AppRoutingModule in Angular? What are the advantages of using a routing module?
Q240. Does routing modules import order matter in Angular?
Q241. What is the use of RouterOutlet in Angular?
Q242. What is the difference between RouterLink vs. RouterLinkActive in Angular?
Q243. Can you skip the Routing Module in Angular? Do we need a Routing Module always?
Q244. What is the use of router.navigate in Angular?
Q245. What is the Activated Route in Angular?
Angular Interview Questions and Answers: Part 21
Q235. What are the wildcard routes in Angular? Why it is important in any application?
In Angular, wildcard routes are used to handle undefined or unknown routes in an application. If the URL doesn't match any predefined routes then it causes the router to throw an error and crash the app. In this case, you can use the wildcard route. When the router encounters a URL that doesn’t match any defined routes, it can redirect or display a specific component designated for handling such scenarios.
A well-functioning application should gracefully handle when users attempt to navigate to a part of your application that does not exist. To add this functionality to your application, you set up a wildcard route. The Angular router selects this route any time the requested URL doesn't match any router paths.
To set up a wildcard route, you can define a route with a path consisting of two asterisks (**). This route will be selected by the router if the requested URL doesn’t match any of the paths defined in the earlier configuration.
const routes: Routes = [
{ path: 'User', component: UserComponent },
{ path: '**', component: PageNotFoundComponent }
];
The last route with the path of ** is a wildcard route. The two asterisks, **, indicate to Angular that this route's definition is a wildcard route. For the component property, you can define any component in your application.
The router selects the route with a first-match wins strategy. Because a wildcard route is the least specific route, place it last in the route configuration.
Common choices include an application-specific PageNotFoundComponent, which you can define to display a 404 page to your users; or a redirect to your application's main component. A wildcard route is the last route because it matches any URL.
Q236. What are URL Redirects in Angular? How can you set up redirects in the Angular?
In Angular, URL redirects are used to navigate the user to a different URL or route within the application. This is useful when you want to redirect the user to a different page after they have completed an action or when you want to redirect them to a different page based on certain conditions.
To redirect the user to a different route within your Angular application, you can use the Router service. This service provides methods for navigating between routes in your application.
External URL Redirection:
To redirect the user to a different external URL, you can use the window.location.href property. This property sets or returns the entire URL of the current page, including the protocol, hostname, and query string.
window.location.href = 'https://www.techpointfunda.com';
Alternatively, you can use the document.location.href as well. The document.location.href is a property that returns the entire URL of the current page. In Angular, you can use window.location.href to redirect to an external URL. To use this, you need to import DOCUMENT from @angular/common.
import { DOCUMENT } from '@angular/common';
constructor(@Inject(DOCUMENT) private document: Document)
{
this.document.location.href = 'https://www.techpointfunda.com';
}
Internal URL Redirection:
To redirect the user to a different route within your Angular application, you can use the Router service. This service provides methods for navigating between routes in your application.
import { Router } from '@angular/router';
constructor(private router: Router) {
this.router.navigate(['/home']);
}
Alternatively, to set up a redirect, you can configure a route with the path you want to redirect from, the component you want to redirect to, and a pathMatch value that tells the router how to match the URL.
Use of Internal Redirect:
When the application launches, the initial URL in the browser bar is by default: localhost:4200
That doesn't match any of the hard-coded routes which means the router falls through to the wildcard route and displays the PageNotFoundComponent.
However, the application needs a default route to a valid page. The application should navigate there as if the user clicked the "Home" link or pasted localhost:4200/home into the address bar.
So you need to add a redirect route that translates the initial relative URL (' ') to the default path (/home) you want. You must add the default route somewhere above the wildcard route. It's just above the wildcard route in the following example.
const routes: Routes = [
{ path: 'User', component: UserComponent },
{ path: '', redirectTo: '/home-component', pathMatch: 'full' },
{ path: '**', component: PageNotFoundComponent }
];
A redirect route requires a pathMatch property to tell the router how to match a URL to the path of a route. When pathMatch is set to full, Angular will search for the exact path in the URL in the routes array. This is useful when you want to redirect the user to a specific page or route.
Here notice that this redirect precedes the wildcard route. Here, empty path: ' ' means to use the initial relative URL (' ').
Q237. What is the pathMatch in Angular? What is the default value of the pathMatch?
In Angular, pathMatch is a property that is used to define how Angular matches the requested URL against the configured routes.
There are two possible values for pathMatch: prefix and full. The default behavior of Angular is to use prefixes for all routes.
Full PathMatch:
When pathMatch is set to full, Angular will search for the exact path in the URL in the routes array. This is useful when you want to redirect the user to a specific page or route.
Technically, pathMatch = 'full' results in a route hit when the remaining, unmatched segments of the URL match ' '.
For example, if you want to redirect the user to the home page when they visit your website’s root URL, you can use full pathMatch:
{ path: '', redirectTo: '/home-component', pathMatch: 'full' }
Prefix PathMatch:
The other possible pathMatch value is 'prefix' which tells the router to match the redirect route when the remaining URL begins with the redirect route's prefix path. This is the default in Angular.
Q238. What is the difference between pathMatch and redirectTo in Angular?
In Angular, pathMatch, and redirectTo are two properties that are used to configure the behavior of the router.
The pathMatch is a property that is used to define how Angular matches the requested URL against the configured routes. There are two possible values for pathMatch: prefix and full. The default behavior of Angular is to use prefix for all routes.
On the other hand, redirectTo is a property that is used to redirect the user to a different route when they visit a specific URL. For example, if you want to redirect the user from login to the dashboard:
{ path: 'login', redirectTo: '/dashboard'}
Q239. What is AppRoutingModule in Angular? What are the advantages of using a routing module?
The routing module, often called the AppRoutingModule, replaces the routing configuration in the root or feature module. AppRoutingModule is a NgModule in Angular that is used to configure the routes of an Angular application. It is generated by the Angular CLI when you create a new application with routing enabled.
The routing module is helpful as your application grows and when the configuration includes specialized guard and resolver functions.
Some developers skip the routing module when the configuration is minimal and merge the routing configuration directly into the companion module (for example, AppModule).
Most applications should implement a routing module for consistency. It keeps the code clean when the configuration becomes complex. It makes testing the feature module easier. Its existence calls attention to the fact that a module is routed. It is where developers expect to find and expand routing configuration.
Advantages of Routing Module:
The primary advantage of using a routing module in Angular is that it helps you manage the navigation and routing of your application in a structured and organized way. By defining your routes in a separate module, you can keep your code modular and easy to maintain.
You can also use lazy loading to load only the necessary modules and components when they are needed, which can improve the performance of your application.
Another advantage of using a routing module is that it allows you to define guards to protect your routes from unauthorized access. Guards are used to control access to certain routes based on user authentication or other criteria. For example, you can use a guard to prevent unauthenticated users from accessing certain parts of your application.
Q240. Does routing modules import order matter in Angular?
Yes, if you have multiple routing modules and you want to register and use them at the application root level, the order of import in the import array matters. The order of route configuration is important because the router accepts the first route that matches a navigation request path.
The router selects the route with a first-match wins strategy. Because a wildcard route is the least specific route, place it last in the last route configuration.
imports: [
BrowserModule,
HttpClientModule,
UserRoutingModule,
AppRoutingModule
]
Here notice that in the module imports array, the AppRoutingModule is last and comes after the UserRoutingModule. When all routes were in one AppRoutingModule, you put the default and wildcard routes last, after the /user route, so that the router had a chance to match a URL to the /user route before hitting the wildcard route and navigating to "Page not found".
Each routing module augments the route configuration in the order of import. If you listed AppRoutingModule first, the wildcard route would be registered before the user routes. The wildcard route which matches every URL would intercept the attempt to navigate to a user route.
Q241. What is the use of RouterOutlet in Angular?
The router outlet serves as a placeholder where the routed components are rendered. The RouterOutlet is a directive from the router library and it acts as a placeholder that marks the spot in the template where the router should display the components for that outlet. The router outlet is used as a component.
Router Outlet is a directive in Angular that is used to mark where in a template, a matched component should be inserted. It is available from the @angular/router package and is used by the router to insert a matched component in a template.
The router outlet is used to create multiple views/pages in an application. The app template acts like a shell of your application, and any element you add to the shell will be rendered in each view. Only the part marked by the router outlet will be changed between views.
You can also name the router outlet using the name property. You can have multiple outlets in your Angular template. The unnamed outlet is the primary outlet in your app, and except for the primary outlet, all the other outlets must have a name. You can specify the router outlet where you want to insert the route component using the outlet.
You can add a router outlet to the main application template that exists in the src/app/app.component.html file associated with the root App component.
<nav>
<ul>
<li><a routerLink="/home-component" routerLinkActive="active" ariaCurrentWhenActive="page">HOME </a></li>
<li><a routerLink="/user-component" routerLinkActive="active" ariaCurrentWhenActive="page">USER</a></li>
</ul>
</nav>
<router-outlet></router-outlet>
Q242. What is the difference between RouterLink vs. RouterLinkActive in Angular?
RouterLink and RouterLinkActive are both directives in Angular that are used to navigate between different views of an application. In summary, RouterLink is used to navigate to a specific route, while RouterLinkActive is used to highlight the active link in the navigation menu.
RouterLink:
RouterLink is a directive that is used to navigate to a specific route when clicked. It is used to bind a clickable HTML element to a route. You can use it to navigate to a specific route by binding it to a string or an array of strings that represent the route path.
You can also use it to bind to a variable that represents the route path. When the user clicks on the element, the router navigates to the specified route.
<nav>
<ul>
<li><a routerLink="/home-component" routerLinkActive="active" ariaCurrentWhenActive="page">HOME </a></li>
<li><a routerLink="/user-component" routerLinkActive="active" ariaCurrentWhenActive="page">USER</a></li>
</ul>
</nav>
RouterLinkActive:
RouterLinkActive is a directive that is used to add a CSS class to an element when the link is active. It is used to highlight the active link in the navigation menu. You can use it to add a CSS class to the element when the link is active.
The directive adds the class when the link is active and removes it when the link is inactive. You can also use it to add a CSS class to the element when the link is partially active.
RouterLinkActive is a directive that toggles CSS classes for active RouterLink bindings based on the current RouterState. The Router will add CSS classes when this link is active and remove when the link is inactive.
Q243. Can you skip the Routing Module in Angular? Do we need a Routing Module always?
In angular the Routing Module is a design choice. You can skip the routing Module (AppRoutingModule) when the configuration is simple and merge the routing configuration directly into the companion module (AppModule). However, it is recommended when the configuration is complex and includes specialized guard and resolver services.
The Angular router is an external, optional NgModule called RouterModule. It is not mandatory to use the routing module in Angular, but it is highly recommended to use it for better organization and maintainability of your application.
The routing module provides a way to map URLs to components in your application. It also provides a way to navigate between different views and components in your application.
If you choose not to use the routing module, you will have to manually handle navigation between different components and views in your application. This can be a tedious and error-prone process, especially for larger applications.
Q244. What is the use of router.navigate in Angular?
In Angular, router.navigate() is a method of the Router class that allows you to navigate to a specific route programmatically. It is used to navigate to a specific route by specifying the route path and any required parameters.
Router.navigate specifies a root URL through relative navigation. This function can be used to navigate in Angular. You can also pass additional parameters to the route by specifying them as an object in the second parameter of the router.navigate() method.
import { Component } from '@angular/core';
import { Router } from '@angular/router';
@Component({
selector: 'app-home',
templateUrl: './home.component.html',
styleUrls: ['./home.component.sass']
})
export class HomeComponent {
constructor(private router: Router) {}
goToRoute() {
this.router.navigate(['/home']);
}
}
In the above example, router.navigate(['/home']) navigates to the route with the path home.
Q245. What is the Activated Route in Angular?
In Angular, the ActivatedRoute is a service that provides access to information about the currently activated route. It is part of the @angular/router module and is used to extract information about the current route, such as route parameters, query parameters, and URL segments.
The ActivatedRoute service is typically injected into a component’s constructor using Angular’s dependency injection system. ActivatedRoute contains the information about a route associated with a component loaded in an outlet. It can also be used to traverse the router state tree. The ActivatedRoute will be injected as a router service to access the information.
import { Component } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
@Component({
selector: 'app-activated-route-demo',
templateUrl: './activated-route-demo.component.html',
styleUrls: ['./activated-route-demo.component.sass']
})
export class ActivatedRouteDemoComponent {
constructor(private route: ActivatedRoute) {}
ngOnInit() {
this.route.paramMap.subscribe(params => {
console.log('Route Parameters : ' + params ); // Access route parameters here
});
this.route.queryParamMap.subscribe(params => {
console.log('Query Parameters : ' + params ); // Access query parameters here
});
}
}
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