The Most Common AngularJS Interview Questions 2023
Here are a few potential interview questions related to AngularJS:
1.Can you explain the purpose of the “ng-app” directive in AngularJS? How does it work?
In AngularJS, the “ng-app” directive is used to define an AngularJS application. It specifies the root element of the application, and it is typically used to kick off the application by telling AngularJS which part of the HTML contains the application code.
The “ng-app” directive is usually placed on the root element of the HTML document, like this:
Alternatively, you can specify the name of the AngularJS module that should be used to bootstrap the application by setting the value of the “ng-app” directive to the module name:
Once the “ng-app” directive is in place, AngularJS will automatically bootstrap the application when the page is loaded. This means that AngularJS will initialize the application by creating the injector and compiling the root element of the application.
I hope this helps to clarify the purpose of the “ng-app” directive in AngularJS! Let me know if you have any additional questions.
2.How does AngularJS implement two-way data binding, and why is it useful?
In AngularJS, two-way data binding is implemented using a combination of the “ng-model” directive and the “{{ }}” binding syntax. This allows changes made to the view (e.g., through user input) to be automatically reflected in the model, and changes made to the model to be automatically reflected in the view.
For example, consider the following code:
In this example, the “ng-model” directive binds the value of the input field to the “user.name” property of the model. The “{{ }}” binding syntax is used to display the value of the “user.name” property in the view. With two-way data binding, any changes made to the input field will be automatically reflected in the “user.name” property of the model, and any changes made to the “user.name” property will be automatically reflected in the input field.
Two-way data binding is useful because it makes it easy to keep the view and the model in sync, without having to write explicit code to handle updates in either direction. This can help to reduce the amount of code you need to write, and it can make it easier to build applications that are responsive to user input.
3.Can you discuss the role of controllers in an AngularJS application, and how they are used to connect the view and the model?
In AngularJS, controllers are used to control the behavior of the view and the model. They are defined as JavaScript functions that are used to augment the scope of an AngularJS application.
Controllers are typically used to define the behavior of a particular part of the view. For example, you might define a controller for a login form that handles the submission of the form and performs authentication. In this case, the controller would be responsible for updating the model (e.g., by setting a “loggedIn” flag) and updating the view (e.g., by displaying an error message or redirecting the user to a different page).
Controllers are typically associated with a view through the use of the “ng-controller” directive. For example:
In this example, the “Login Controller” controller is associated with the div element using the “ng-controller” directive. The controller’s functions and properties are then available to the view within the div element and can be accessed using the “ng-” prefix (e.g., “ng-submit” and “ng-model”).
4.How does AngularJS handle dependency injection, and why is it important?
In AngularJS, dependency injection is a way to provide a required dependency to a component (such as a service, controller, or filter) as an argument to its constructor function. AngularJS uses dependency injection to provide services to components, as well as to make it easier to test components by injecting mock dependencies in place of real ones.
To use dependency injection in AngularJS, you first define the dependencies that a component requires as arguments to its constructor function. For example:
In this example, the “MyController” function requires the “$scope” and “MyService” dependencies. These dependencies will be provided to the controller by AngularJS at runtime, using the names of the arguments as a hint to determine which dependencies are needed.
Dependency injection is important in AngularJS because it helps to make the code more modular and easier to maintain. It also makes it easier to test components in isolation, by allowing you to inject mock dependencies in place of real ones.
5.Can you discuss the difference between a template-driven and reactive forms approach in Angular?
In Angular, there are two approaches to building forms: template-driven forms and reactive forms.
Template-driven forms are built using the template syntax in the Angular template. They are easy to use and familiar to developers with a background in HTML, but they can be more difficult to test and debug compared to reactive forms.
With template-driven forms, you define the form and the validation rules in the template, using directives such as “ngModel” and “required”. For example:
In this example, the “ngModel” directive binds the value of the input field to a property on the component’s scope, and the “required” attribute specifies a validation rule that requires the field to be non-empty.
Reactive forms, on the other hand, are built using a reactive programming model. They are more flexible and powerful than template-driven forms, but they may require more code to set up and are less familiar to developers with a background in HTML.
With reactive forms, you define the form and the validation rules in the component class, using the FormControl, FormGroup, and FormArray classes. For example:
In this example, a FormGroup is created with a FormControl for the “username” field, and the “required” validator is applied to the control. The form can then be used in the template with the “formGroup” directive:
6.How does Angular’s router work, and how can it be used to build single-page applications?
In Angular, the router is a service that allows you to define a configuration for how the application should navigate between different views. It is designed to make it easy to build single-page applications (SPAs), where the entire application runs in a single web page and navigation is achieved by changing the view without reloading the page.
To use the router in an Angular application, you first need to import the RouterModule and configure the routes for your application. This is typically done in the root module of your application (e.g., AppModule).
For example:
In this example, the routes configuration defines two routes: one for the root path (“/”) and one for the “about” path. Each route is associated with a component that should be displayed when the route is activated.
Once the routes are configured, you can use the router in the template to display the active view and enable navigation between views. This is typically done using the “routerLink” directive to define links and the “router-outlet” directive to display the active view:
In this example, the “routerLink” directive is used to define links that navigate to the specified routes, and the “router-outlet” directive is used to display the active view in the main content area of the page.
7.Can you discuss the use of observables in Angular, and how they can be used to manage asynchronous data?
In Angular, observables are a way to handle asynchronous data and events. They are used to represent a stream of values or events that can be processed over time, and they are an important part of the ReactiveX library for reactive programming.
Observables can be used in Angular to manage asynchronous data in a variety of ways. For example, you can use an observable to retrieve data from an HTTP service and display it in the template, like this:
In this example, the “data$” property is an observable that retrieves data from the “DataService”. The “async” pipe is used to subscribe to the observable and display the data in the template when it is available.
Observables can also be used to handle events in the template. For example, you can use the “fromEvent” operator to create an observable from a DOM event:
These are just a few examples, but there are many other potential questions that could be asked about Angular and its features.
