Angular Interview Questions and Answers - Part 23
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 famous as a frontend technology so it is very important from 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 23rd part of the Angular Interview Questions and Answer series.
I will highly recommend that you visit the following parts before continuing to this part:
Angular Interview Questions and Answers - Part 23
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In this part we will discuss the following Important Angular Interview Questions:
Angular Interview Questions and Answers: Part 23
Q256. What are the different router events used in Angular?
Angular Router provides a set of events that are triggered when the router navigates from one route to another. During each navigation, the Router emits navigation events through the Router.events property allowing you to track the lifecycle of the route.
These events can be used to perform tasks such as logging, tracking, and updating the application’s state. The sequence of router events is as follows:
1. NavigationStart: Triggered when the Angular router starts the navigation.
2. RouteConfigLoadStart: Triggered when the Router lazy loads a route configuration.
3. RouteConfigLoadEnd: Triggered after a route has been lazy-loaded.
4. RoutesRecognized: Triggered when the Router parses the URL and the routes are recognized.
5. GuardsCheckStart: Triggered when the Router begins the Guard's phase of routing.
6. ChildActivationStart: Triggered when the Router begins activating a route’s children.
7. ActivationStart: Triggered when the Router begins activating a route.
8. GuardsCheckEnd: Triggered when the Router finishes the Guards phase of routing successfully.
9. ResolveStart: Triggered when the Router begins the Resolve phase of routing.
10. ResolveEnd: Triggered when the Router finishes the Resolve phase of routing successfully.
11. ChildActivationEnd: Triggered when the Router finishes activating a route’s children.
12. ActivationEnd: Triggered when the Router finishes activating a route.
13. NavigationEnd: Triggered when navigation ends successfully.
14. NavigationCancel: Triggered when navigation is canceled. This is due to a Route Guard returning false during navigation.
15. NavigationError: Triggered when navigation fails due to an unexpected error.
16. Scroll: An event that represents a scrolling event.
You can listen to these events and find out when the state of the route changes.
Q257. What are Pipes in Angular? What are the different types of Pipes?
In Angular, Pipes are used to transform data before displaying it in the view. Pipes are simple functions that accept an input value and return a transformed value. They can be used to format strings, numbers, dates, and other types of data.
Pipes are simple functions designed to accept an input value, process, and return as an output, a transformed value in a more technical understanding.
Angular provides several built-in pipes such as DatePipe, UpperCasePipe, LowerCasePipe, CurrencyPipe, DecimalPipe, and PercentPipe. These pipes can be used to format data in a variety of ways. For example, DatePipe can be used to format dates, CurrencyPipe can be used to format currency values, and DecimalPipe can be used to format numbers.
- Pipes are defined using the pipe “|” symbol.
- Pipes can be chained with other pipes.
- Pipes can be provided with arguments by using the colon (:) sign.
<p>User Name: {{ name | uppercase }}</p>
In addition to the built-in pipes, you can also create your own custom pipes to transform data in a way that is specific to your application. To create a custom pipe, you need to define a class that implements the PipeTransform interface and provide a transform method that accepts an input value and returns a transformed value. Pipes are extremely useful as we can use them throughout our application after declaring them just once and registering them with the Angular framework.
Q258. What is the purpose of an async pipe?
In Angular, the AsyncPipe is a built-in pipe that subscribes to an Observable or Promise and returns the latest value it has emitted. The AsyncPipe is used to handle asynchronous data in Angular applications. It automatically subscribes to an Observable or Promise and updates the view when new data is emitted.
The AsyncPipe is useful because it simplifies the process of subscribing to an Observable or Promise and updating the view when new data is emitted. It also helps to prevent memory leaks by automatically unsubscribing from the Observable or Promise when the component is destroyed.
To use the AsyncPipe, you simply need to add it to your template and pass in the Observable or Promise that you want to subscribe to. The AsyncPipe subscribes to an observable or promise and returns the latest value it has emitted.
<p>The current time is {{ time$ | async }}</p>
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