Sure! Here are 80 Angular interview questions and answers:
1. What is Angular?
Angular is a popular open-source JavaScript framework for building web applications. It allows developers to create dynamic and responsive applications with a structured approach using HTML, CSS, and TypeScript.
2. What are the key features of Angular?
The key features of Angular are:
- Two-way data binding
- Dependency injection
- Modular architecture
- Component-based development
- Routing
- Form handling
- Code generation with Angular CLI
3. What is the difference between AngularJS and Angular?
AngularJS, also known as Angular 1.x, is a JavaScript-based framework, while Angular (Angular 2+) is a complete rewrite of AngularJS using TypeScript. Angular introduces many improvements, including a more modular architecture, better performance, and enhanced tooling.
4. What is TypeScript?
TypeScript is a statically typed superset of JavaScript that compiles to plain JavaScript. It adds features like static types, classes, interfaces, and modules to JavaScript, providing better tooling and maintainability.
5. What is a component in Angular?
A component in Angular is a building block that encapsulates the template, styles, and behavior of a part of the user interface. It consists of a TypeScript class and an associated HTML template.
6. What is a module in Angular?
A module in Angular is a container for organizing related components, directives, services, and other code. It helps to keep the application structured and allows for better code separation and reusability.
7. What is data binding in Angular?
Data binding is the automatic synchronization of data between the model and the view. In Angular, it can be achieved using one-way binding (from model to view or vice versa) or two-way binding, where changes in the model or view are automatically propagated to the other.
8. What is the difference between interpolation and property binding?
Interpolation is a way to bind values dynamically into the HTML template using double curly braces ({{ }}). Property binding, on the other hand, allows you to bind a property of an element to a value in the component using square brackets ([ ]).
9. What is dependency injection in Angular?
Dependency injection is a design pattern in which the dependencies of a class or component are provided externally rather than being created within the class itself. Angular uses dependency injection to manage the creation and sharing of dependencies across components.
10. How do you implement dependency injection in Angular?
In Angular, you can implement dependency injection by declaring the dependencies in the constructor of a class or component. Angular's DI system will then automatically resolve and inject the dependencies when creating instances of the class.
11. What is the purpose of the NgModule decorator in Angular?
The NgModule decorator is used to define and configure Angular modules. It specifies the metadata for the module, such as imports, exports, declarations, providers, and bootstrap components.
12. What is a directive in Angular?
A directive in Angular is a class that modifies the behavior or appearance of a DOM element. There are three types of directives in Angular: component, structural, and attribute directives.
13. What is the difference between structural and attribute directives?
Structural directives change the structure of the DOM by adding or removing elements. They are denoted by an asterisk (*) prefix, such as *ngIf and *ngFor. Attribute directives, on the other hand, modify the behavior or appearance of an existing element, like [ngStyle] and [ngClass].
14. What is Angular CLI?
Angular CLI (Command Line Interface) is a command-line tool that helps developers create, build, and manage Angular applications. It provides a set of commands for generating components, services, modules, and other artifacts, as well as building and running the application.
15. How do you create a new Angular application using Angular CLI?
To create a new Angular application using Angular CLI, you can run the following command:
```
ng new my-app
```
This will create a new directory called "my-app" with the basic structure and files of an Angular application.
16. What is the purpose of the Angular router?
The Angular router is used for navigation and routing within an Angular application. It allows you to define routes, associate them with components, and navigate between different views.
17. How do you define routes in Angular?
Routes in Angular can be defined using the RouterModule and the Routes array. Each route consists of a path and a component to be rendered when that path is accessed.
18. What is lazy loading in Angular?
Lazy loading is a technique in Angular that allows you to load modules and their associated components only when they are actually needed, rather than loading everything upfront. This can improve the initial loading time of the application.
19. What is an Angular service?
An Angular service is a class that provides specific functionality and can be shared across multiple components. It is typically used to encapsulate common logic, data retrieval, or interaction with external services.
20. How do you create a service in Angular?
To create a service in Angular, you can use the Angular CLI command:
```
ng generate service my-service
```
This will generate a service file with the specified name, which you can then edit and provide your desired functionality.
21. What is an Angular pipe?
An Angular pipe is a feature that allows you to transform and format data within a template. It takes an input value and returns a modified value, which can be used for display or further processing.
22. What are some built-in pipes in Angular?
Angular provides several built-in pipes, including:
- DatePipe: for formatting dates
- UpperCasePipe and LowerCasePipe: for converting text to uppercase or lowercase
- DecimalPipe and CurrencyPipe: for formatting numbers and currencies
- SlicePipe: for extracting a subset of an array or string
23. How do you create a custom pipe in Angular?
To create a custom pipe in Angular, you need to create a new class and implement the PipeTransform interface. The class should have a transform method that takes an input value and any optional parameters and returns the transformed value.
24. What is Angular's HttpClient module used for?
The HttpClient module in Angular is used for making HTTP requests to a server. It provides methods for performing common HTTP operations like GET, POST, PUT, DELETE, etc., and also supports features like request and response interception, error handling, and observables for handling asynchronous responses.
25. How do you perform an HTTP GET request using HttpClient?
To perform an HTTP GET request using HttpClient, you can use the `get` method, like this:
```typescript
import { HttpClient } from '@angular/common/http';
constructor(private http: HttpClient) { }
getData() {
return this.http.get('/api/data');
}
```
26. What is Angular's Reactive Forms module used for?
The Reactive Forms module in Angular is used for handling and validating form inputs in a reactive and declarative way. It provides a set of classes and directives for building and managing complex forms.
27. How do you perform form validation in Angular?
In Angular, you can perform form validation by using built-in validators or by creating custom validators. Validators can be applied to individual form controls or to a group of controls. You can also display validation errors in the template based on the form control's validity state.
28. What is the difference between template-driven forms and reactive forms in Angular?
Template-driven forms rely on directives and two-way data binding to handle form inputs, while reactive forms are built using reactive programming principles
and are entirely driven by code. Reactive forms offer more control, flexibility, and testability compared to template-driven forms.
29. How do you implement routing in Angular?
To implement routing in Angular, you need to define routes in the app module or a separate routing module. You also need to add a `<router-outlet>` directive in your template to specify where the routed components should be displayed. Additionally, you can use the routerLink directive to create navigation links.
30. What is Angular's ViewChild decorator used for?
The ViewChild decorator in Angular is used to obtain a reference to a child component, directive, or element in the template. It allows you to access the properties and methods of the referenced element/component from the parent component.
31. What is Angular's ngFor directive used for?
The ngFor directive in Angular is used for rendering a template for each item in a collection. It allows you to iterate over arrays, objects, and other iterable data sources and dynamically generate content based on each item.
32. What is Angular's ngIf directive used for?
The ngIf directive in Angular is used for conditionally rendering elements in the template. It evaluates an expression and displays the associated content only if the expression evaluates to true.
33. How do you share data between components in Angular?
There are several ways to share data between components in Angular, including:
- Input and Output properties: Parent components can pass data to child components using input properties and receive output events using output properties.
- Services: Components can share data through a common service that is injected into both components.
- State management libraries: Libraries like NgRx or Redux can be used for managing application state and sharing data between components.
34. What is Angular's ngStyle directive used for?
The ngStyle directive in Angular is used for dynamically applying inline styles to an element based on the values of expressions in the component. It allows you to modify the appearance of an element based on conditions or data values.
35. What is Angular's ngClass directive used for?
The ngClass directive in Angular is used for dynamically applying CSS classes to an element based on the values of expressions in the component. It allows you to conditionally add or remove CSS classes from an element.
36. What is the Angular TestBed used for?
The TestBed in Angular is a utility for configuring and creating an Angular testing module. It provides methods for configuring dependencies, creating component instances, and interacting with the testing environment.
37. What is Angular's async pipe used for?
The async pipe in Angular is used for subscribing to and displaying the result of an asynchronous operation in the template. It automatically subscribes and unsubscribes to an Observable or Promise, and updates the template whenever the value changes.
38. What is Angular's ElementRef used for?
The ElementRef in Angular is a wrapper around a native DOM element. It allows you to access and manipulate the properties and methods of the native element directly. However, it should be used with caution, as direct DOM manipulation bypasses Angular's change detection mechanism.
39. What is Angular's Renderer2 used for?
The Renderer2 in Angular is a service that provides a set of methods for manipulating elements and attributes of the DOM in a way that is safe and compatible with server-side rendering. It should be used instead of direct DOM manipulation with ElementRef whenever possible.
40. What is Angular's ng-content directive used for?
The ng-content directive in Angular is used for projecting content into a component from its parent component. It allows you to create reusable components that can be customized with different content.
41. What is the purpose of Angular's trackBy function?
The trackBy function in Angular is used in ngFor loops to improve performance when rendering a list of items. It helps Angular identify unique items in the list and efficiently update the
DOM when the list changes, instead of re-rendering the entire list.
42. What is Angular Universal?
Angular Universal is a technology that allows you to run Angular applications on the server, providing server-side rendering (SSR). SSR improves the initial loading time and enables better search engine optimization (SEO) and social media sharing for Angular applications.
43. What are Angular interceptors?
Angular interceptors are a feature that allows you to intercept and modify HTTP requests and responses globally. Interceptors can be used for tasks such as adding headers, handling errors, or modifying the request/response payload.
44. How do you handle errors in Angular HTTP requests?
In Angular, you can handle errors in HTTP requests by subscribing to the Observable returned by the HTTP methods and providing error handling logic in the error callback. You can also use the catchError operator to handle errors and return a new Observable or throw an error.
45. What is Angular's ngZone used for?
The ngZone service in Angular is used to handle zones, which are execution contexts that allow you to control change detection and asynchronous operations. ngZone is often used when working with third-party libraries or APIs that are not aware of Angular's change detection.
46. What is Angular's ContentChild decorator used for?
The ContentChild decorator in Angular is used to obtain a reference to a specific content child element or directive inside a component. It allows you to access the properties and methods of the referenced child element/directive from the parent component.
47. What is Angular's ContentChildren decorator used for?
The ContentChildren decorator in Angular is used to obtain a reference to multiple content child elements or directives inside a component. It allows you to access the properties and methods of the referenced children from the parent component as a QueryList.
48. What is Angular's ngTemplateOutlet directive used for?
The ngTemplateOutlet directive in Angular is used for dynamically rendering a template in the component's view. It allows you to define a template and then use it multiple times with different data or conditions.
49. What is Angular's ngTemplateRef used for?
The ngTemplateRef in Angular is a reference to an embedded template that can be rendered using the ngTemplateOutlet directive. It provides access to the template's content and allows you to dynamically render it with different data or conditions.
50. What is Angular's ngAfterViewInit lifecycle hook used for?
The ngAfterViewInit lifecycle hook in Angular is called after the component's view and child views have been initialized. It is commonly used for tasks that require access to the DOM or manipulating child components.
51. What is Angular's ngOnInit lifecycle hook used for?
The ngOnInit lifecycle hook in Angular is called after the component has been initialized and its properties have been bound. It is commonly used for initialization tasks, such as retrieving data from a service.
52. What is Angular's ngDoCheck lifecycle hook used for?
The ngDoCheck lifecycle hook in Angular is called during every change detection cycle and allows you to perform custom change detection logic. It is often used to detect changes in complex data structures or trigger specific actions based on changes.
53. What is Angular's ngOnDestroy lifecycle hook used for?
The ngOnDestroy lifecycle hook in Angular is called when a component is about to be destroyed. It is commonly used to perform cleanup tasks, such as unsubscribing from subscriptions or releasing resources.
54. What is Angular's ngZone.run() method used for?
The ngZone.run() method in Angular is used to execute a function inside the Angular zone. It is often used when working with third-party libraries or APIs that are not aware of Angular's change detection, ensuring that the changes triggered by the function are properly detected and applied.
55. What is Angular's ngModel directive used for?
The ngModel directive in Angular is used for two-way
data binding between an input element and a property in the component. It allows you to bind the input's value to a component property and automatically update the property when the input value changes, and vice versa.
56. What is Angular's @HostBinding decorator used for?
The @HostBinding decorator in Angular is used to bind a property of a directive or component to a property of its host element. It allows you to modify the host element's properties or attributes based on the state or values of the directive/component.
57. What is Angular's @HostListener decorator used for?
The @HostListener decorator in Angular is used to listen to events on the host element of a directive or component. It allows you to define a method that will be executed when a specified event occurs on the host element.
58. What is Angular's ngClass directive used for?
The ngClass directive in Angular is used for dynamically adding or removing CSS classes from an element based on the values of expressions in the component. It allows you to conditionally apply different styles to an element.
59. What is Angular's ngSwitch directive used for?
The ngSwitch directive in Angular is used for conditionally rendering elements based on the value of an expression. It allows you to define multiple cases and associate them with different templates that will be rendered based on the value of the expression.
60. What is Angular's ng-container used for?
The ng-container element in Angular is a structural directive that provides a placeholder in the template for rendering content conditionally or iteratively. It does not render any HTML element itself and is often used in combination with other directives like ngIf or ngFor.
61. What is Angular's @Input decorator used for?
The @Input decorator in Angular is used to define an input property in a component. It allows the property to receive values from its parent component, enabling communication and data sharing between components.
62. What is Angular's @Output decorator used for?
The @Output decorator in Angular is used to define an output property in a component. It allows the component to emit events to its parent component, notifying it of certain actions or changes.
63. What is Angular's ng-content directive used for?
The ng-content directive in Angular is used to project content from a parent component into the template of a child component. It allows the parent component to define the content that will be displayed within the child component's template.
64. What is Angular's ng-template directive used for?
The ng-template directive in Angular is used to define a template that can be reused and rendered in multiple places using the ngTemplateOutlet directive. It allows you to create flexible and reusable templates within your Angular application.
65. What is Angular's ViewChild decorator used for?
The ViewChild decorator in Angular is used to get a reference to a child component, directive, or element in the parent component. It allows the parent component to access the properties and methods of the child element/component.
66. What is Angular's ViewEncapsulation used for?
The ViewEncapsulation in Angular is used to define how styles are scoped and applied to components. It allows you to encapsulate component styles and prevent them from affecting other components by applying specific encapsulation modes like Emulated, ShadowDom, or None.
67. What is Angular's Renderer2 used for?
The Renderer2 in Angular is a service that provides a set of methods for manipulating elements and attributes of the DOM in a way that is safe and compatible with server-side rendering. It is used instead of direct DOM manipulation with ElementRef to ensure compatibility across different rendering environments.
68. What is Angular's platform-browser-dynamic used for?
The platform-browser-dynamic module in Angular is used to dynamically bootstrap and render an Angular application in a browser environment. It provides the necessary APIs and functions to compile and load an Angular module
at runtime.
69. What is Angular's ng-template used for?
The ng-template element in Angular is used to define a template that can be reused and rendered conditionally in the component's view. It allows you to create reusable content that can be included or excluded based on certain conditions.
70. What is Angular's ngZone used for?
The ngZone service in Angular is used to handle zones, which are execution contexts that allow you to control change detection and asynchronous operations. It is often used when working with third-party libraries or APIs that are not aware of Angular's change detection, ensuring that the changes triggered by these libraries are properly detected and applied.
71. What is Angular's router-outlet used for?
The router-outlet directive in Angular is used to render the component associated with the current route. It acts as a placeholder in the template and dynamically displays the component content based on the activated route.
72. What is Angular's ActivatedRoute used for?
The ActivatedRoute service in Angular is used to access information about the currently activated route. It provides access to route parameters, query parameters, and other route-related data, allowing components to react and respond to route changes.
73. What is Angular's ngModel directive used for?
The ngModel directive in Angular is used for two-way data binding between a form control element and a component property. It allows you to bind the value of the form control to a property in the component and automatically update both the control and the property when either one changes.
74. What is Angular's ngOnInit lifecycle hook used for?
The ngOnInit lifecycle hook in Angular is called after the component has been initialized and its inputs have been bound. It is commonly used for initialization tasks, such as retrieving data from a service or performing setup operations.
75. What is Angular's ngStyle directive used for?
The ngStyle directive in Angular is used for dynamically applying inline styles to an element based on the values of expressions in the component. It allows you to modify the appearance of an element based on conditions or data values.
76. What is Angular's ngClass directive used for?
The ngClass directive in Angular is used for dynamically applying CSS classes to an element based on the values of expressions in the component. It allows you to conditionally add or remove CSS classes from an element.
77. What is Angular's ng-content directive used for?
The ng-content directive in Angular is used for projecting content from a parent component into the template of a child component. It allows the parent component to define the content that will be displayed within the child component's template.
78. What is Angular's ng-container used for?
The ng-container element in Angular is a structural directive that provides a placeholder in the template for rendering content conditionally or iteratively. It does not render any HTML element itself and is often used in combination with other directives like ngIf or ngFor.
79. What is Angular's @HostBinding decorator used for?
The @HostBinding decorator in Angular is used to bind a property of a directive or component to a property of its host element. It allows you to modify the host element's properties or attributes based on the state or values of the directive/component.
80. What is Angular's @HostListener decorator used for?
The @HostListener decorator in Angular is used to listen to events on the host element of a directive or component. It allows you to define a method that will be executed when a specified event occurs on the host element.
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