Here is a list of possible interview questions of Angular, along with answers to help you prepare for your interview: Angular Interview Questions
1. What is Angular and what are its features?
Angular is a JavaScript framework for building web applications. Its features include two-way data binding, modular architecture, reusable components, and a powerful template language.
2. What is the difference between AngularJS and Angular?
AngularJS is the first version of Angular and Angular is the second version. Angular is a complete rewrite of AngularJS with improved performance, better modularity, and improved features.
3. What is a directive in Angular?
A directive in Angular is a custom HTML element or attribute that provides additional functionality to an Angular application. Directives allow developers to extend HTML syntax.
4. What is a component in Angular?
A component in Angular is a class that defines a reusable piece of the user interface. Components control a portion of the screen and interact with the user through events and two-way data binding.
5. What is the difference between a component and a directive in Angular?
A component defines a reusable piece of the user interface and has its own template and logic. A directive extends HTML syntax to add additional functionality to an Angular application.
6. What is a service in Angular?
A service in Angular is a class that contains business logic that can be reused across multiple components in an Angular application. Services are used for tasks such as making HTTP requests or logging to the console.
7. What is two-way data binding in Angular?
Two-way data binding in Angular allows for changes in the model to be reflected in the view and vice versa. This makes it easy for developers to keep the user interface in sync with the data model.
8. What is a template in Angular?
A template in Angular is a HTML file that defines the structure of a component’s user interface. The template can contain bindings to the component’s properties and events.
9. What is the difference between a template and a component in Angular?
A template defines the structure of a component’s user interface while a component defines the logic and behavior of the user interface.
10. What is the difference between Angular and React?
Angular is a full-fledged framework while React is a JavaScript library. Angular has a large set of built-in features and a more complex structure, while React focuses on a simpler approach and more flexibility.
11. What is the role of NgModule in Angular?
NgModule is a class that defines a module in Angular. It declares which components, directives, and services belong to the module, as well as providing configuration options such as imports and exports.
12. What is a route in Angular? Angular Interview Questions
A route in Angular is a URL path that maps to a component. Routing is used to navigate between different parts of an Angular application.
13. What is the difference between a component and a module in Angular?
A component defines a reusable piece of the user interface and has its own template and logic. A module in Angular defines a set of components, directives, and services that belong together.
14. What is the difference between @Input and @Output in Angular?
@Input is a decorator that is used to bind data from a parent component to a child component. @Output is a decorator that is used to emit an event from a child component to a parent component.
15. What is dependency injection in Angular?
Dependency injection in Angular is a design pattern where a component receives its dependencies from an external source instead of creating them itself. This makes it easier to maintain and test components.
16. What is the difference between promises and observables in Angular?
Promises in Angular represent a single value that will be available in the future, either a success value or an error. Observables in Angular represent a stream of values that can be processed over time.
17. What is the role of HttpClient in Angular?
HttpClient is a class in Angular that is used to make HTTP requests. It provides a simplified and unified API for making network requests.
18. What is the difference between reactive and template-driven forms in Angular?
Reactive forms in Angular are programmatically driven and are used when a dynamic and complex form is required. Template-driven forms in Angular are easy to use and are used when a simple form is required.
19. What is lazy loading in Angular?
Lazy loading in Angular is a technique for loading parts of an application only when they are needed. This improves the initial loading time of an application and helps reduce the size of the main JavaScript bundle.
20. What is a pipe in Angular?
A pipe in Angular is a mechanism for transforming data before it is displayed to the user. Pipes can be used to format dates, currency, and perform other common data transformations.
21. What is a guard in Angular?
A guard in Angular is a service that is used to control access to a route. Guards can be used to prevent unauthorized access to a route or to prompt the user for confirmation before navigating away from a route.
22. What is AOT in Angular?
AOT stands for Ahead-of-Time compilation. In AOT, Angular compiles the application before it is run, resulting in improved startup performance and reduced payload size.
23. What is the difference between ngFor and ngForOf in Angular?
ngFor and ngForOf are both Angular directives that are used to iterate over a collection of items. ngFor is an alias for ngForOf, which is the current recommended directive for use in Angular applications.
24. What is a resolver in Angular?
A resolver in Angular is a service that is used to fetch data before a route is activated. Resolvers can be used to load data asynchronously, ensuring that the required data is available before the route is activated.
25. What is the difference between RouterLink and RouterLinkActive in Angular?
RouterLink is an Angular directive that is used to navigate to a route when a user clicks on a link. RouterLinkActive is an Angular directive that adds a CSS class to the element when the route is active.
26. What is the difference between ngIf and ngSwitch in Angular?
ngIf is an Angular directive that is used to conditionally render an element based on a condition. ngSwitch is an Angular directive that is used to conditionally render elements based on a value.
27. What is the difference between ngModel and [(ngModel)] in Angular?
ngModel is an Angular directive that is used to bind a value to a form control. [(ngModel)] is a two-way data binding syntax that binds a value to a form control and updates the value whenever the user inputs a new value.
28. What is a singleton in Angular?
A singleton in Angular is a service that is created only once and shared among all components that depend on it. Singletons are used to share data and state across an Angular application.
29. What is a reactive form in Angular?
A reactive form in Angular is a programmatically driven form that is used when a dynamic and complex form is required. Reactive forms provide more control over form validation and data management compared to template-driven forms.
30. What is the difference between ngOnInit and constructor in Angular?
ngOnInit is an Angular lifecycle hook that is called after a component is initialized. The constructor in Angular is used to create and initialize an instance of a component. The constructor is called before ngOnInit and is used to initialize the component’s properties and dependencies.
31. What is the difference between a factory and a service in AngularJS?
In AngularJS, both factories and services are used to create reusable objects that can be injected into controllers, directives, and other services. However, there are some key differences between the two:
- Definition: A factory is defined as a function that returns an object, while a service is defined as a constructor function that creates and returns an object.
- Instantiation: Factories are instantiated by calling the function and services are instantiated by using the “new” keyword.
- Singleton: Services are singletons, which means that a new instance of the service is created only once and the same instance is reused throughout the application. While a factory can be configured to return a singleton, it also allows for returning a new instance of the object for each call.
- Lazy loading: Services are instantiated lazily, which means that they are not instantiated until they are first used. Factories are instantiated immediately when they are first used.
- Use cases: Services are used when you need to share data between controllers, while factories are used when you need to return a value or an object that can be used by other components.
In summary, Services are singleton objects that are instantiated lazily while Factories are instantiated immediately and can return a singleton or new object each time it’s called.
32. What is dependency injection in AngularJS?
In AngularJS, dependency injection is a mechanism that allows components, such as controllers, services, and directives, to acquire their dependencies in a decoupled way. Instead of creating dependencies inside the component, they are passed in from the outside.
Dependency injection (DI) allows AngularJS to provide components with their dependencies automatically, rather than requiring the component to look for or create its own dependencies. This makes the components more reusable and easier to test, as well as making the application more modular and easier to understand.
The core of dependency injection in AngularJS is the $injector service, which is responsible for creating and managing instances of the different components. When a component is defined, it specifies its dependencies using an array of strings, and when it is instantiated, the $injector service looks up the specified dependencies and passes them in as arguments to the component’s constructor function.
In summary, Dependency injection allows AngularJS to provide components with their dependencies automatically by injecting them into the component instead of the component creating them. This makes the components more reusable and easier to test and also makes the application more modular and easier to understand.
33.What is the difference between a structural directive and an attribute directive in Angular?
A structural directive changes the structure of the DOM by adding or removing elements, while an attribute directive changes the appearance or behavior of an element.
34. How does AngularJS implement routing?
In AngularJS, routing is implemented using the ngRoute module, which is a separate module that needs to be included and added as a dependency for your AngularJS application.
The ngRoute module provides the $routeProvider service, which is used to configure the routes for your application. The $routeProvider service has methods such as when() and otherwise() to configure the routes.
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35. What is a directive in AngularJS?
In AngularJS, a directive is a custom HTML element or attribute that can be used to extend the functionality of the HTML language. Directives are used to bind behavior to elements in the DOM, and are typically used to create reusable UI components.
AngularJS provides several built-in directives such as ng-app, ng-controller, ng-model, ng-repeat, and ng-bind. These directives are used to define the application scope, define the controller for a view, bind data to form elements, repeat elements, and bind data to elements respectively.
You can also create custom directives in AngularJS. Custom directives can be used to extend the functionality of HTML elements, create reusable UI components, and encapsulate complex logic.
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36. How do you create a custom directive in AngularJS?
In AngularJS, you can create a custom directive by using the .directive method on the AngularJS module. The .directive method takes two arguments: the name of the directive and a factory function that returns an object that defines the behavior of the directive.
Here is an example of how to create a custom directive called “myDirective” in AngularJS:
var app = angular.module('myApp', []);
app.directive('myDirective', function() {
return {
restrict: 'E',
template: '<div>This is my directive</div>',
replace: true
};
});
37. What is the difference between a compile and a link function in a directive?
In AngularJS, a directive can have two functions: a compile function and a link function. These functions are used to define the behavior of the directive and are executed at different stages of the directive’s lifecycle.
The compile function is called once when the directive is first compiled by AngularJS. The purpose of the compile function is to modify the DOM structure before it is linked to the scope. The compile function can be used to make changes to the element on which the directive is used, such as adding or removing elements, or changing the attributes of the element.
The link function is called once for each instance of the directive, after the directive’s template has been cloned and added to the DOM. The purpose of the link function is to link the directive’s behavior to the scope. The link function can be used to register event listeners, set up data bindings, and perform other logic that is specific to the directive’s behavior.
38. How can you use animation in AngularJS?
In AngularJS, you can use animations by using the ngAnimate module, which is a separate module that needs to be included and added as a dependency for your AngularJS application.
The ngAnimate module provides a way to apply CSS classes and styles during the different stages of an animation, such as when an element is added to the DOM, removed from the DOM, or updated. To use animations, you’ll need to include the ngAnimate module and the CSS classes that define the animations in your application.
39. How does AngularJS handle exception handling?
In AngularJS, exception handling can be done using the $exceptionHandler service. This service can be used to handle uncaught exceptions that occur in the application. The $exceptionHandler service can be configured with a custom handler function that will be called when an exception is thrown.
Here’s an example of how to configure the $exceptionHandler service in an AngularJS application
app.config(function($provide) {
$provide.decorator('$exceptionHandler', function($delegate) {
return function(exception, cause) {
$delegate(exception, cause);
// custom error handling code
};
});
});
40. What is ngIf ?
ngIf is a built-in directive in AngularJS (and Angular) that allows you to conditionally add or remove an element from the DOM based on a boolean expression.
The ngIf directive is used to bind a boolean expression to an element. If the expression is true, the element is added to the DOM, otherwise, the element is removed from the DOM.
Here is an example of how to use the ngIf directive in an AngularJS template:
<div ng-if="showMessage">
<p>This message will be displayed if showMessage is true</p>
</div>41. What is ngFor ?
ngFor is a directive in Angular that allows you to loop through an array or an object and create a template for each item in that collection. It is used to display a list of items in a component’s template. The syntax for using ngFor typically looks like this:
<div *ngFor="let item of items">
{{item}}
</div>
This will loop through the “items” array and create a new div element for each item in the array, and the value of each item will be displayed within the div.
42. What ngSwitch ?
ngSwitch is a directive in AngularJS (version 1.x) that allows you to conditionally render content based on the value of an expression. It is typically used in conjunction with the ngSwitchCase and ngSwitchDefault directives to define the different cases and the default behavior. The ngSwitch directive is placed on an element, and the value of the expression is compared to the values of the ngSwitchCase directives. If a match is found, the corresponding content is displayed. If no match is found, the content defined by the ngSwitchDefault directive is displayed.
43. What is Angular pipes ?
Angular pipes are a way to transform data in an Angular application. They are a simple way to format data for display in a template. Pipes can be used in templates to format data, such as converting a date to a specific format, formatting a currency, or converting a string to uppercase or lowercase. Angular comes with a number of built-in pipes like date, currency, uppercase, lowercase, etc. and also you can create your own custom pipes. Pipes are denoted by using the '|' character in a template expression, followed by the pipe name.
44. What is the ngClass directive in Angular?
The ngClass directive in Angular is an attribute directive that allows you to add or remove CSS classes based on conditions.
45. What is the ngStyle directive in Angular?
The ngStyle directive in Angular is an attribute directive that allows you to set inline styles on an element based on conditions.
46. What is the ngModel directive in Angular?
The ngModel directive in Angular is an attribute directive that allows you to create two-way data binding.
47. What is the ngOnInit lifecycle hook in Angular?
The ngOnInit lifecycle hook in Angular is called after the component has been initialized, and is a good place to perform any initialization logic.
48. What is a service worker in Angular?
A service worker in Angular is a script that runs in the background and can be used for tasks such as caching, push notifications, and background sync.
49. What is a template in Angular?
A template in Angular is a simple HTML file that defines the layout and structure of a component’s view.
50. What is a module in Angular?
A module in Angular is a way to organize an application into cohesive blocks of functionality.
51. How does data binding work in Angular?
Data binding in Angular allows properties of a component to be bound to expressions in the template, so that when the component’s properties change, the template updates automatically.
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