As the Angular framework becomes more widely used, there will likely be a greater need for Angular developers. This set of more than 40+ AngularJS interview questions and answers is intended for freshers and experienced developers. Check out our AngularJS course syllabus to get started.
AngularJS Interview Questions for Freshers
To aid in your preparation, here are 40 AngularJS interview questions and answers:
1. What is Angular?
Google created the robust JavaScript framework Angular to develop dynamic web apps. It provides an organized development method that facilitates the creation of intricate, expandable, and maintained programs.
2. What are Angular’s fundamental ideas?
The fundamental concepts of AngularJS are:
- Components: Angular application building blocks that contain a certain UI element.
- Templates: HTML documents that specify how a component’s view should be organized.
- Modules: A logical collection of parts, pipes, directives, and services.
- Metadata: Used to give the Angular framework extra information and to adorn classes.
- Services: Shareable, reusable business logic among components.
- Dependency Injection: This design pattern adds dependencies to services and components.
- Data Binding: The process by which data is automatically synchronized between the display and the model.
- Routing: The process by which an application switches between views.
3. What distinguishes AngularJS from Angular?
A comprehensive redesign of AngularJS, Angular offers notable enhancements in developer experience, performance, and modularity.
TypeScript vs. JavaScript, component-based architecture vs. MVC, improved dependency injection, and improved performance are some of the main distinctions.
4. Describe the idea of data binding in Angular.
With Angular, data binding enables data synchronization between the TypeScript class and the component’s template automatically. There are mostly two types:
- Interpolation: Using the {{ }} syntax, values from the component are bound to the template.
- Property Binding: Using the [property]=”expression” syntax, values from the component are bound to the properties of DOM elements.
- Event Binding: This involves utilizing the syntax (event)=”method()” to bind DOM events to methods within the component.
- Two-Way Data Binding: Using [(ngModel)] syntax, this technique combines property and event binding to enable bidirectional data flow between the component and the template.
5. What is a directive in Angular?
Custom HTML elements or attributes known as directives increase HTML’s capability. They can be applied to alter the behavior of pre-existing DOM elements or to produce reusable user interface components.
6. Describe a component’s lifecycle hooks.
Methods known as “lifecycle hooks” are invoked at particular stages of a component’s lifecycle. Important lifecycle hooks consist of:
- ngOnInit(): After the component has been initialized, ngOnInit() is called.
- ngOnChanges(): When input properties change, ngOnChanges() is called.
- ngOnDestroy(): Before the component is deleted, ngOnDestroy() is called.
7. In Angular, how is data passed across components?
Data can be passed between components in many ways:
- Input Properties: Data can be passed from a parent component to a child component using the @Input() decorator.
- Output Properties: Events can be sent from a child component to a parent component using the @Output() decorator.
- Shared Services: Components can communicate with one another by using a shared service.
8. Define a module in Angular.
A logical collection of parts, directives, pipes, and services is called a module. It offers a method for structuring and organizing an Angular application and specifies the range of dependencies.
9. Explain Dependency injection.
A design pattern called dependency injection enables services and components to rely on abstractions as opposed to specific implementations. Dependencies are automatically injected into components and services via Angular’s dependency injection framework.
10. What does Angular’s routing mean?
You can specify distinct routes for various views in your application using routing. The relevant component appears when a user navigates to a particular URL.
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11. How are routes defined in Angular?
The RouterModule and Routes array are used to define routes. A path and a component that has to be loaded make up each route.
12. What are Angular template-driven forms?
HTML templates are used in template-driven forms to specify validation criteria and form controls. To manage form validation, Angular offers built-in directives such as ngModel, ngRequired, and ngPattern.
13. What are Angular’s model-driven forms?
TypeScript classes are used in model-driven forms to specify validation rules and form models. Form groups and controls can be created using Angular’s FormBuilder API.
14. In Angular, how do you submit HTTP requests?
HTTP queries like GET, POST, PUT, and DELETE are made using the HttpClient service.
15. What does Angular unit testing entail?
Unit testing entails testing distinct services and components separately. Angular offers the ComponentFixture class for component testing and the TestBed class for building test environments.
16. What is Angular’s end-to-end testing?
Testing the complete application from the viewpoint of the user is known as end-to-end testing. The Protractor framework for end-to-end testing is offered by Angular.
17. What distinguishes await from async in Angular?
To write asynchronous code synchronously, utilize the keywords async and await. A promise is returned by async methods, and execution is halted until the promise is resolved using await.
18. What is RxJS?
A reactive programming library called RxJS enables you to interact with asynchronous data streams. It is widely used in Angular to manage event streams, HTTP requests, and other asynchronous tasks.
19. In Angular, what is a pipe?
Pure functions, known as pipes, convert input data into output data. They are employed to carry out various changes, including formatting and filtering data.
20. What distinguishes ngOnInit() from ngDoCheck()?
- ngOninit: Only called once when the component is initialized.
- ngDoCheck: On each change detection run, ngDoCheck is called right after ngOnchanges(); on the first run, it is called right after ngOninit().
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AngularJS Interview Questions and Answers for Experienced
21. How do OnPush and Default change detection systems vary from one another?
The primary distinction between the Default and OnPush change detection mechanisms in Angular is when they look for changes:
- OnPush: When an event occurs, an input reference changes, or markForCheck is manually triggered, OnPush checks for changes. In large applications, this approach enhances performance and is more effective.
- Default: Every change detection cycle includes default checks for modifications to all components and their templates. Performance-wise, this approach is usually acceptable because Angular can complete these checks rapidly.
22. What is the purpose of ChangeDetectionStrategy.OnPush?
By lowering the number of checks and updates that Angular’s change detection system makes, the OnPush change detection strategy in Angular aims to enhance application performance:
How it operates: Reference types are treated as immutable objects by the OnPush strategy, which only looks for changes when the @Input() data supplied to it has a new reference.
When it’s beneficial: Large component trees and sophisticated applications are best suited for the OnPush approach.
Advantages:
The OnPush approach is capable of:
- Make it easier to trace bugs.
- Optimize applications using intricate data sets.
- Accelerate Angular’s ability to recognize changes.
CheckAlways, Angular’s default change detection strategy, looks for modifications in all components and their templates during each change detection cycle.
23. What is the difference between providedIn: ‘root’ and providedIn: ‘any’?
Here is the difference between providedIn: ‘root’ and providedIn: ‘any’:
provideIn:root: The service is made available across the application when providedIn is set to “root,” indicating that it is being supplied at the root level. When providedIn is left unspecified, this is the default value.
provideIn:Any: The injector for the NgModule that gets the resolution.
24. What is the difference between ViewChild and ViewChildren?
The primary distinction between @ViewChild and @ViewChildren in Angular is that the former makes a single reference to a native DOM element, whilst the latter makes a list of references to several native DOM elements:
- @ViewChild: One reference to a native DOM element is returned by @ViewChild.
- To access a child component, directive, or DOM element from a parent component class, use @ViewChild.
- @ViewChild will immediately update its reference if it dynamically moves to a new element.
- @ViewChildren: A QueryList containing pointers to several native DOM items is returned by @ViewChildren. To access more than one kid, use @ViewChildren.
Child component classes and their properties can be accessed using the decorators @ViewChild and @ViewChildren. They resemble inheritance. To work with the component class or its DOM element, you can utilize these pointers.
25. What distinguishes ContentChild from ContentChildren?
The primary distinction between Angular’s ContentChild and ContentChildren decorators is that the former returns a single child, whilst the latter returns an array of references called a QueryList:
- ContentChild: ContentChild gives back a single child directive or component that corresponds to the given selector. It is usually applied when the child component or directive appears only once.
- ContentChildren: A QueryList, an array of references to elements that have been added to the component’s template via content projection.
To access child components or directives that are projected into the component using the element, use either ContentChild or ContentChildren. They function similarly to the decorators ViewChild and ViewChildren.
26. How does Angular handle HTTP request errors?
You can utilize the built-in error-handling features in Angular to deal with HTTP request problems, such as:
- ErrorHandler: Add a unique handler to your AppModule.
- HTTP Interceptor: Use request and response intercepting to handle HTTP failures worldwide.
- Component-Level Error Handling: Put error management into practice at the component level, particularly for asynchronous or crucial tasks.
You may use an HTTP interceptor to handle failures worldwide by following these steps:
- Construct a service and put the ErrorHandler interface into use.
- Use the @angular/core ErrorHandler class to deliver the service.
- Build an HTTP Interceptor
- Give your AppModule the interceptor.
An interceptor can also be used to carry out operations in your application both before and after each HTTP request. For example, you can log failures using a functional interceptor:
- Describe the interceptor.
- Make the interceptor available everywhere.
Any error produced on the Observable response stream is wrapped in an HttpErrorResponse by Angular. Either a wrapped Error object or the server’s error response is contained in the error attribute.
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27. What is the purpose of the @HostListener decorator?
You may listen for and react to events on the host element of a component or directive using Angular’s @HostListener decorator:
- What it does: It specifies a DOM event to watch for and offers a handler function to execute in response to that event.
- Why it’s beneficial: Managing events such as keyboard inputs, mouse movements, clicks, scrolls, and more
- How it operates: A component method is bound to a particular event so that it runs when the event is triggered.
Angular 2+’s HostListener Decorator is one of the two Angular decorators that can be helpful with custom directives: @HostListener. You can set properties on the element or component that hosts the directive using the other decorator, @HostBinding.
28. Explain the use of the @HostBinding decorator.
You can set properties of the host element from the directive class using Angular’s @HostBinding decorator. The state of the directive or component can be synchronized with the host element’s properties with the help of this decorator.
The @HostBinding decorator can be used for the following purposes:
- Modify the host element’s style attributes, including its width, height, color, border, and margin.
- Configure any additional host element internal characteristics.
- Allow the host element’s properties, classes, or styles to be updated dynamically.
The name of the host element property that you wish to set to a value in the directive is the only parameter that the @HostBinding decorator accepts.
Examples: @HostBinding(‘style.color’), @HostBinding(‘style.border-color’), @HostBinding(‘class.active’), @HostBinding(‘disabled’), and @HostBinding(‘attr.role’).
29. What is the difference between NgZone and setTimeout?
SetTimeout: Unrestrained Memory Use Because timers keep references to the component, using SetTimeout() or setInterval() without deleting them can cause memory leaks.
Example
import { Component, OnInit } from ‘@angular/core’;
@Component({
selector: ‘app-leak-example’,
template: `
<h1>{{ counter }}</h1>
`
})
export class LeakExampleComponent implements OnInit {
counter = 0;
ngOnInit() {
setTimeout(() => {
this.counter++;
}, 1000);
}
}
NgZone: Zone awareness and change detection are handled by the Angular service NgZone. Through the use of NgZone, we guarantee that asynchronous processes are carried out inside the Angular zone, enabling appropriate change detection and user interface updates.
Example
import { Component, OnDestroy, NgZone } from ‘@angular/core’;
@Component({
selector: ‘app-example’,
template: `
<h1>{{ counter }}</h1>
`
})
export class ExampleComponent implements OnDestroy {
counter = 0;
timer: any;
constructor(private ngZone: NgZone) {}
ngOnInit() {
this.ngZone.runOutsideAngular(() => {
this.timer = setInterval(() => {
this.ngZone.run(() => {
this.counter++;
});
}, 1000);
});
}
ngOnDestroy() {
clearInterval(this.timer);
}
}
30. State the differences between observables and promises in Angular.
Observables and promises differ primarily in the following ways:
- Execution: While promises run instantly, observables are postponed, meaning that computation begins when they are subscribed to.
- Values: Whereas promises only offer one value, observables can offer several values over time.
- Adaptability: Promises are clear-cut and basic, whereas observables are more adaptable and capable of handling intricate data manipulation.
- Cancellation: Promises are eager and cannot be canceled, while observables may.
- Transformation: While promises have “.then()” clauses that can change values after the work is finished, observable values can also be changed using operators in the subscription.
In JavaScript, observables and promises are both mechanisms for managing asynchronous operations. The particular requirements of the project and the asynchronous tasks that must be completed will determine which option is best.
31. What is the difference between Subject and BehaviorSubject?
- When you don’t need an initial value and are only concerned with future values, use Subject.
- When you need an initial value and want new subscribers to get the most recent value right away, use BehaviorSubject.
32. What is the purpose of the ReplaySubject in AngularJS?
When you need to repeat a single event or a sequence of events, you often utilize ReplaySubject.
ReplaySubject is a useful method to utilize in cases where an event may never even occur because, unlike BehaviorSubject, it does not require a default value. Suppose you need to process user events, and you lazy load a library.
33. What is the difference between the takeUntil and takeWhile operators?
Until it is told to stop, the takeUntil(notifier) continues to emit the values. While values satisfy the predicate, takeWhile(predicate) returns the value. When finished, all of the stops emitting.
34. What is the difference between the switchMap and mergeMap operators?
The primary distinction between the switchMap and mergeMap operators is that the former cancels earlier requests, whereas the latter permits them to be completed.
- switchMap only takes into account the most recent request and cancels earlier ones. HTTP GET calls are frequently used with it. For instance, switchMap can cancel earlier calls and subscribe to the most recent one while a user is entering an input box.
- mergeMap transmits answers as they come in and lets all requests complete. There is no assurance of the order of responses. A shopping cart’s contents are a good example of a mergeMap use case.
35. What is the purpose of the debounceTime operator?
The debounceTime operator postpones a source’s value emission for a predetermined time:
Purpose: It’s employed to stop events from happening too often. This is helpful if you wish to stay away from:
- Button spamming by users
- Overloading a server with requests
- Data extraction based on partial ideas
How it operates:
- When the allotted time has elapsed, the debounceTime operator emits the most recent value it has recorded:
- The timer is reset, and the previous value is dropped if a new value comes before the allotted time.
- Only the most current notice from each emission burst is sent out by the debounceTime operator.
When it’s beneficial: For form validation, the debounceTime operator is frequently utilized. It can be used, for instance, to wait for a user to finish typing before verifying a street name. Typically, a user input debounce duration of 300 to 400 ms is ideal.
36. What is the purpose of the debounceTime operator?
The debounceTime operator postpones a source’s value emission for a predetermined period:
Purpose: It’s employed to stop events from happening too often. When handling quick sequences of events, such as when a user is filling out a form, this can be helpful.
How it operates: After the allotted time has elapsed, the debounceTime operator emits the most recent value it has recorded. The timer is reset, and the previous value is dropped if a new value is received before the allotted period.
Advantages: DebounceTime can be used to
- Enhance user experience
- Avoid making pointless API calls.
- Make sure that the user’s whole idea is used to retrieve the data.
Typically, a user input debounce duration of 300 to 400 ms is ideal.
37. What is the purpose of the distinctUntilChanged operator?
Values in an observable stream that are exactly the same as the value that comes before it can be filtered out using the distinctUntilChanged operator. It makes sure that redundant or repetitive values are ignored and that only unique and new values are passed downstream.
38. What is the purpose of the filter operator?
When applying a filter, a filter operator defines how fields are compared. It is used to tie parameters to one another and functions similarly to a verb in a phrase. “Is greater than,” “is equal to,” and “is less than” are a few instances of filter operators.
39. What does AngularJS’s “validation of data” mean to you?
Form validation and filling are enhanced by AngularJS. AngularJS offers form validation on the client side. It notifies the user of the current status after verifying the input fields (text-area, input, and select) and the form.
Additionally, it contains information regarding whether or not the input fields have been touched or altered. The directions listed below can be used to monitor errors:
- $dirty: The value has been altered, it says.
- $invalid: It indicates that the entered value is not valid.
- $error: The precise inaccuracy is stated.
Additionally, we can disable the browser’s built-in form validation by using novalidate with a form declaration.
40. How can you use AngularJS to conceal an HTML tag element when a button is clicked? Create a program that does the same thing.
The ng-click directive, which manages the condition used to modify the tag’s display in the ng-hide directive, can be utilized to accomplish this.
<!DOCTYPE html>
<html>
<head>
<meta chrset=”UTF 8″>
<title>Button Click Hide</title>
</head>
<body>
<script src=”https://code.angularjs.org/1.6.9/angular.js”></script>
<script src=”https://code.jquery.com/jquery-3.3.1.min.js”></script>
<div ng-app=”buttonDemo” ng-controller=”buttonDemoController”>
<button ng-click=”hideTag()”>Hide IntervieBit</button>
<div ng-hide=”hideFlag”>InterviewBit</div>
</div>
<script type=”text/javascript”>
var app = angular.module(‘buttonDemo’,[]);
app.controller(‘buttonDemoController’,function($scope){
$scope.hideFlag = false;
$scope.hideTag = function(){
$scope.hideFlag = true;
}
});
</script>
</body>
</html>
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Conclusion
We hope these AngularJS interview questions and answers help you understand the theory concepts deeply. To ace your Angular interview, don’t forget to research Angular documentation, practice code challenges, and keep up with the newest trends and best practices. Join SLA for the best AngularJS training in Chennai.
