70+ AngularJS Interview Questions & Answers You Must Know!

Angular JS is a web framework and tool used for developing applications. It is based on JavaScript as its basic language. This framework made the testing and development of applications much simpler and is hence most known for this purpose. Angular JS is mainly employed in the creation of expandable web applications (more specifically in the front end of the MEAN stack and MongoDB). It is because of this that the demand for programmers skilled in Angular JS is high. If you are applying for a job in this domain, check out the Angular JS interview questions and answers we have listed here.

Angular JS Interview Questions: The Fundamentals

In this section of the AngularJS interview question bank, you will find questions that test your basic foundational knowledge of the web framework. So let's get started!

Q1. What is your understanding of AngularJS and what are its key features?

AngularJS is a well-known open-source JavaScript framework for creating dynamic, single-page, and large-scale enterprise web application programs. Developed by Google, AngularJS uses HTML as its primary template language, which is enhanced with directives to represent application components. AngularJS combines the power of JavaScript with the Model-View-Controller (MVC) architecture, enabling developers to build client-side logic effectively. This approach results in scalable, maintainable web applications that are compatible with various web browsers. 

Q2. What are some of the advantages of using AngularJS over other frameworks?

There are numerous advantages that make AngularJS a popular choice for building modern web applications, especially those that require dynamic user interfaces, complex data interactions, and a clean, maintainable codebase. Some of them include:

• Open-Source: AngularJS is an open-source framework maintained by Google and a community of developers. Being open-source means that the framework is continuously improved, updated, and supported by a large community of contributors.
• Single Page Application (SPA) Creation: AngularJS facilitates the development of single-page applications (SPAs), where the entire application is contained within a single web page. This approach provides a more fluid user experience, as the application can dynamically update sections of the page without requiring a full page reload.
• MVC Design Pattern: AngularJS follows the Model-View-Controller (MVC) design pattern, which promotes a clear separation of concerns. This separation allows for easier maintenance, testing, and scalability of the application codebase.
• Predefined Form Validations: AngularJS provides built-in support for form validations, allowing developers to define validation rules for form fields declaratively in the HTML. This feature simplifies the validation process and ensures that user input is accurate and consistent.
• Cross-Browser Compatibility: AngularJS is designed to work seamlessly across different web browsers, ensuring that the application functions consistently and reliably regardless of the user's choice of browser.

Q3. What are some of the disadvantages of using AngularJS over other frameworks?

While AngularJS offers numerous advantages for web development, it also has some drawbacks that as a developer we should consider:

• Steep Learning Curve: AngularJS has a steep learning curve, especially for beginners or developers who are new to front-end frameworks. Its complex concepts and unique features, such as directives and dependency injection, can be challenging to grasp initially.
• Performance Overhead: AngularJS can introduce performance overhead, especially in large-scale applications, due to its extensive features and dynamic nature. In some cases, excessive use of two-way data binding can impact performance, requiring careful optimization.
• Complexity of Directives: While directives are a powerful feature of AngularJS, they can also introduce complexity, especially when creating custom directives with complex behavior. Understanding the life-cycle and scope of directives can be challenging for developers.
• SEO Challenges: AngularJS applications may face challenges with search engine optimization (SEO) due to their reliance on JavaScript for rendering content. While AngularJS has improved in this aspect with tools like Angular Universal, SEO considerations are still important.
• Versioning and Migration: AngularJS has undergone significant changes over the years, with major updates introducing breaking changes. This can pose challenges for projects that need to migrate between different versions of AngularJS, requiring careful planning and effort.

Q4. What are some of the AngularJS's standout characteristics?

Some of the key features of the web framework AngularJS are:

• Data Binding: AngularJS implements two-way data binding, which means that changes in the model (JavaScript variables) are automatically reflected in the view (HTML), and vice versa. This simplifies the process of keeping the UI in sync with the underlying data.
• Scope: Scopes in AngularJS are objects that refer to the application model. They act as a glue between the controller and the view, holding the data that needs to be presented to the user.
• Dependency Injection: AngularJS has a built-in dependency injection subsystem that helps in making components of the application more modular, reusable, and testable. It allows the developer to declare the dependencies of a component, and AngularJS takes care of providing them when needed.
• Filters: Filters in AngularJS allow the developer to format the value of an expression for display to the user. They can be used in controllers, services, and directives to format data in a particular way before presenting it to the user.
• Services: Services in AngularJS are singletons that are used to organize and share code across the application. They are used for tasks such as data manipulation, logging, and communicating with servers.
• Factories: Factories are a type of service in AngularJS that are used to create objects or functions that can be injected into other components of the application. They are often used for creating instances of objects that need to be shared across multiple parts of the application.
• Expressions: Expressions in AngularJS are used to bind data to HTML. They are written inside double curly braces {{ }} and are evaluated against the current scope. They can contain literals, operators, and variables and are often used to display dynamic content in the view.
• Modules: Modules in AngularJS are containers for different parts of an application, such as controllers, services, filters, and directives. They help in organizing the application into smaller, reusable components and provide a way to configure the application.
• Controllers: Controllers in AngularJS are JavaScript functions that are used to control the data flow in the application. They are responsible for initializing the scope, attaching model data to the scope, and providing functions for manipulating the model.
• Directives: Directives in AngularJS are markers on a DOM element that tell AngularJS's HTML compiler (i.e., $compile) to attach a specified behavior to that DOM element. Or even transform the DOM element and its children. 
• Validators: AngularJS provides a set of built-in validators that can be used to validate form input fields. These validators can be used to enforce rules such as required fields, minimum and maximum length, email format, etc.
• Providers: Providers in AngularJS are a way to create and configure services before they are used in an application. They are used internally by AngularJS to create services, but they can also be used by developers to create their own services with complex configuration needs.

Q5. What are the differences between AngularJS and Angular?

The major differences between AngularJS and Angular and are as follows: 

Q6. What does scope in AngularJS mean? How do scope variables work?

• The scope is a crucial concept that acts as a bridge between the application's controller and its views (HTML). It is an object that holds data and methods that can be accessed by both controllers and views. When the model changes, the scope updates all associated models automatically, ensuring data consistency across the application.
• Technically speaking, a scope is nothing but a JavaScript object with properties & functions that act as an intermediary between model & view components, i.e., a controller to display values on the user interface through expression evaluation or vice versa. This means getting from user input & writing back into Model variables via expressions on HTML page, etc.

The working of scope variable can be explained as follows:

• The scope variable acts as a bridge between the view and the controller. It holds the data that needs to be displayed in the view and provides a mechanism for the controller to interact with the view.
• The scope provides a context for evaluating expressions in the view. AngularJS expressions enclosed in double curly braces ({{ }}) are evaluated against the scope.
• The scope serves as an intermediary for exchanging data between the view and the controller. Data from the controller can be attached to the scope, making it available for display in the view.
• Scopes in AngularJS form a hierarchy based on the DOM structure. Each directive or controller creates its own scope, which inherits properties and methods from its parent scope.
• The scope variable is involved in the digest cycle, which is a mechanism in AngularJS for detecting and propagating changes in the model to the view.

Q7. Explain what is interpolation and its objectives?

Interpolation refers to the process of embedding expressions within double curly braces ({{ }}) in the HTML template. These expressions are evaluated and replaced with their corresponding values from the scope. Interpolation is one of the core features of AngularJS and is used extensively for displaying dynamic data in the view.

The main objectives of interpolation are:

• Dynamic Data Binding: Interpolation allows for seamless binding of data from the model (scope) to the view (HTML).
• Expression Evaluation: Interpolation enables the evaluation of AngularJS expressions within the HTML template. These expressions can be simple variables, complex calculations, or function calls defined in the scope.
• Contextual Evaluation: Interpolation evaluates expressions within the context of the current scope. This means that expressions are resolved based on the properties and methods available in the scope at the time of evaluation.
• Template Rendering: Interpolation is crucial in template rendering process. When AngularJS compiles the HTML template, it scans for interpolation expressions and sets up watchers to track changes in the associated scope properties. If any change is detected, views are automatically updated to reflect the new values.

Q8. What is Data Binding? Describe the various AngularJS data binding techniques.

Data binding refers to the process of connecting an application's user interface (UI) with its underlying data sources. It allows developers to create two-way connections between their applications' user interface and business logic layers, enabling changes in one layer to update the other automatically. This helps ensure that both layers stay synchronized with each other.

Some common data binding techniques in AngularJS are:

• Interpolation: This is the simplest data binding technique where we can bind a property to the HTML element. It uses double-curly braces {{}} to display a component's property value in the view.
• Property/One-way Binding: This data binding procedure helps us set an HTML element's properties and update it dynamically based on changes in AngularJS components. We use [property]= "value" syntax for this purpose, which sets an HTML attribute/property with expression evaluation result given inside quotes (").
• Event Binding: This type of binding allows us to define events on our template that trigger specific methods within our controller when any event occurs, like clicking, hovering, or typing something. We can do this by using parenthesis () around the event name like (click)=" myFunction()".
• Two-Way Data Binding: AngularJS provides a two-way data binding feature where changes made from either side automatically synchronize within both layers (model & view). It supports the ng-model directive, which binds one particular form field model with other parts of the application, such as the business logic layer, etc. So whenever input values change through the user interface, the same is reflected at the application level and vice versa instantly without manual intervention required.

Q9. Explain the scope hierarchy.

Scopes form a hierarchical structure based on the DOM (Document Object Model) hierarchy. This hierarchy mirrors the structure of the HTML elements in the document and is essential for maintaining data binding and managing the flow of data within the application.

• At the top of the scope hierarchy is the root scope, which is created when the AngularJS application is initialized using the ng-app directive. The root scope is associated with the entire HTML document and is used to store global data and functions that need to be accessible throughout the application.
• Below the root scope, child scopes are created for each AngularJS directive that creates a new scope, such as ng-controller, ng-repeat, ng-if, etc.

Child scopes inherit properties and methods from their parent scopes. This means that a child scope has access to all the properties and methods of its parent scope, but any changes made to the child scope do not affect the parent scope directly.

Scopes in AngularJS can emit and listen to events using the $emit, $broadcast, and $on methods. This allows different parts of the application to communicate with each other by sending and receiving messages through the scope hierarchy.

Q10. Explain how MVC pattern is implemented in context with AngularJS?

The Model-View-Controller (MVC) architecture is a design pattern that governs the structure and organization of an application's codebase. AngularJS implements MVC in the following way:

• Model: In AngularJS, the model is represented by JavaScript objects or arrays that are bound to the scope. These objects contain the application's data and are manipulated by controllers to update the state of the application.
• View: The view in AngularJS is defined using HTML templates with embedded AngularJS directives and expressions. Directives such as ng-model, ng-bind, and ng-repeat are used to bind data from the model to the view and to define the structure of the UI.
• Controller: Controllers in AngularJS are JavaScript functions that are responsible for defining the behavior of a specific part of the UI. They are attached to the scope and provide functions and data that are used by the view. Controllers manipulate the model and respond to user actions to update the view.

Q11. What are modules in AngularJS?

Modularity refers to the extent to which interconnected components within a system can be isolated as independent units, capable of functioning autonomously without relying on one another. Angular is known for its modularity as an angular application can consists of multiple modules with lower limit of one and that being called the NgModule. 

When we create a new Angular application using the Angular CLI or any other means, the default NgModule is typically named AppModule. This module is defined in a file named app.module.ts, where ts denotes a TypeScript file. The AppModule serves as the root module of the application. It is the module that is bootstrapped when the Angular application is launched. Bootstrapping refers to the process of initializing the Angular application by loading the root module and its dependencies.

Additionally, Angular modules support importing and exporting of functionalities. This means that we can import components, directives, pipes, and services from other modules into our AppModule to use them in our application. Similarly, we can also export components, directives, pipes, and services from your AppModule to make them available for use in other modules.

Modular architecture facilitates lazy loading, which is a technique used to load modules asynchronously when needed, improving the initial loading time of the application.

Q12. How can AngularJS be integrated with HTML?

We start by including the AngularJS library in your HTML document. We can either download the AngularJS library from the official website or use a content delivery network (CDN) link to include it directly in our HTML file:

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.8.2/angular.min.js"></script>

Then we define an AngularJS module using the angular.module() function. The module serves as a container for different parts of our application, such as controllers, services, directives, etc.

var app = angular.module('myApp', []);

We can create AngularJS controllers using the app.controller() method. Controllers are responsible for defining the behavior of different parts of your application's UI

app.controller('myController', function($scope) {
$scope.message = 'Hello, AngularJS!';
});

Finally we can use AngularJS directives like ng-app and ng-controller to bind our AngularJS module and controllers to specific elements in your HTML

<html ng-app="myApp">
<body ng-controller="myController">
<h1>{{ message }}</h1>
</body>
</html>

Q13. What are directives in AngularJS? (Rewrite)

AngularJS's directives are special attributes that provide a powerful way to bind application data to HTML.

• They are markers on a DOM element that tell AngularJS's HTML compiler ($compile) to attach a specified behavior to that DOM element or even transform the DOM element and its children.
• They enables us to create reusable components and define custom behaviors in a declarative manner, directly within our HTML templates. AngularJS comes with a set of built-in directives, such as ng-model, ng-repeat, ng-show, and ng-click, which provide common functionalities for data binding, iteration, conditional rendering, and event handling.
• In addition to the built-in directives, AngularJS allows us to define our own custom directives. Custom directives are defined using the directive function, which allows us to encapsulate complex behavior and DOM manipulation in a reusable component.

Q14. What are the main distinctions between JavaScript and AngularJS?

AngularJS Interview Questions And Answers: Intermediate

With the basics out of the way, let's have a look at some interview questions that dig a little deeper into your AngularJS knowledge.

Q15. Explain the characteristics of scope.

AngularJS scopes are similar to JavaScript variables, but they come with a few distinct features:

• Properties attached to the scope can be data bound and watched for changes by directives like ng-show, ng-hide, or ng-repeat and expressions. This means that when a property on the $scope object is changed in AngularJS, any part of your HTML page which uses it as an expression will update accordingly.
• Scopes provide APIs ($watch) to observe model mutations (the observer pattern). When using this feature, you should always use function dereferencing so you never mutate models directly and thus avoid unexpected side effects because observers won't fire if there was no actual mutation (= new value differs from the old one).
• Scopes also provide an event system that allows parent scopes to propagate events down the scope chain and decouple communication between controller and directive or controller to controller.

Some characteristics of scope in Angular JS are-

• Scope provides context for expressions: Expressions bind application data and behaviors to HTML elements. Scopes provide a context for those expressions so that AngularJS knows which controllers or models are associated with them.
• Its hierarchical in structure, resembling the DOM tree: The parent scope of any controller is $rootScope, but it can have many child scopes from other nested controllers called Child Controller Scope.
• It acts like a glue between view and controller components: Whenever there is an interaction between the user (view) and the browser (controller), it's mediated by the scope object wherein they pass messages back & forth via events ($emit/broadcast).
• It provides watch facilities to observe model mutations: Watch API provided by angular allows us to monitor specific changes on our models, and corresponding fire callbacks whenever relevant transformation occurs.

Q16. What are the various kinds of directives that AngularJS supports?

Directives are a powerful feature that allows us to extend the functionality of HTML by creating custom HTML elements, attributes, and classes. AngularJS supports several types of directives, each serving a different purpose. Below are some of the directives supported by AngularJS:

• Element Directives: Element directives create custom HTML elements that can be used in the markup. They are typically defined by the name of the custom element enclosed in angular brackets (<my-directive></my-directive>).
• Attribute Directives: Attribute directives modify the behavior or appearance of existing HTML elements by applying custom behavior to them. They are defined using normal HTML attributes prefixed with ng- or a custom prefix.
• Class Directives: Class directives add or remove CSS classes to/from HTML elements based on certain conditions. They are used to dynamically apply styles to elements based on the application state.
• Comment Directives: Comment directives are similar to element directives but are defined using HTML comments. They are less commonly used than other directive types.
• Multi-Element Directives: Multi-element directives operate on a group of elements instead of a single element. They can create, modify, or remove multiple elements at once.

Q17. What are the priority levels of AngularJS directives?

Directive priority is a mechanism used to determine the order in which directives are applied to DOM elements when there are multiple directives competing for the same element. Directive priority is specified using the priority property in the directive definition object.

The priority levels of AngularJS directives range from 0 to 999. A lower priority value indicates a higher priority, meaning that directives with lower priority values are applied before directives with higher priority values. Directives with the same priority are applied in the order in which they are declared in the HTML.

Some key points about directive priority in AngularJS includes:

• Default Priority: If a directive does not specify a priority, it is assigned a default priority of 0.
• Higher Priority: Directives with lower priority values (closer to 0) are executed before directives with higher priority values.
• Execution Order: If multiple directives on an element have the same priority, their execution order is determined by the order in which they appear in the HTML.
• Use Cases: Directive priority is useful when you have multiple directives on the same element that need to interact with each other in a specific order.
• Caution: While directive priority can be useful in certain situations, it is generally recommended to avoid relying on directive priority unless absolutely necessary, as it can make the code harder to understand and maintain.

Q18. What are Angular Expressions?

Angular Expressions are JavaScript-like code snippets written inside an HTML page to display dynamic data, assign values to variables, and evaluate operations. Angular expressions are used with the double braces syntax {{ expression }}. An angular expression can contain literals, operators, or elements of a scope object (variables defined by the application).

Q19. What is the ng-app directive?

The ng-app directive is used in AngularJS development to designate a root element for the app and automatically initializes the application. It can be specified on an HTML element to specify that it should contain either one module or multiple modules of a single-page app. This makes project setup easier than manually bootstrap applications and allows for multiple apps on one page by defining variously named ng-apps within separate HTML elements. Additionally, using an XML namespace prefix helps maintain uniqueness in this environment if more than one app is present.

Q20. What are the uses of the findIndex() method in AngularJS? What is the return value in no value case?

In AngularJS, the findIndex() method is not a built-in method provided by AngularJS itself, but rather a standard JavaScript method available on arrays in modern JavaScript environments (ECMAScript 5 and above). The findIndex() method is used to find the index of the first element in an array that satisfies a provided testing function.

If the element doesn’t exist within the array, then -1 will be returned by findIndex(), which indicates that no value was found.

Q21. In the ng-repeat directive, what does tracking mean?

In the ng-repeat directive, tracking refers to the ability to improve the performance of the directive by assigning a unique identifier to each item in the collection that is being iterated over. This unique identifier helps AngularJS to efficiently update the DOM when the collection changes, especially in scenarios where items are added, removed, or reordered within the collection.

The ng-repeat directive creates a new scope for each item in the collection, and by default, it tracks items in the collection by their internal $$hashKey property.

However, in some cases, such as when the collection items are primitive values (like numbers or strings), using the $$hashKey for tracking can lead to performance issues or unexpected behavior.

Q22. Draw attention to the variations between compile and link in AngularJS.

The compile and link functions are two key parts of the directive definition object that allow us to manipulate the DOM, set up event handlers, and interact with the AngularJS framework during the directive's lifecycle. 

The compile function is used to modify the DOM before it is linked to the scope. It is invoked once for each occurrence of the directive in the HTML template. The compile function is typically used for template manipulation, such as adding, removing, or transforming DOM elements based on the directive's configuration or the application's state.

The link function is used to register DOM listeners and update the DOM with the directive's behavior. It is invoked once for each occurrence of the directive after the DOM has been compiled. The link function is typically used for setting up event listeners, interacting with the scope, and performing other post-compilation tasks.

Advanced-Level Angular JS Interview Questions

If you want to prove your expertise in Angular JS in an interview, then you must prepare for the advanced questions and answers provided below.

Q23. What does AngularJS routing entail? Describe the tasks involved with AngularJS routing.

Routing is a mechanism provided by the AngularJS framework for managing navigation and views in a single-page application (SPA). It allows us to define different routes for our application, each of which corresponds to a different view or state. When the user navigates to a specific route, AngularJS dynamically loads the corresponding view and updates the URL without causing a full page refresh.

Routes are defined using the $routeProvider service, which allows you to specify the URL path, the template or templateUrl to be used for the view, and the controller to handle the view's logic. Routes are typically defined in the application's configuration phase using the config() method of the main application module.

Each route in AngularJS corresponds to a view, which is typically an HTML template that defines the structure and layout of the view and they can be linked to controllers using the controller property in the route definition.. Views can be defined inline using the template property or loaded from external templates using the templateUrl property in the route definition.

AngularJS provides directives like ng-href and ng-click to create links that navigate to different routes within the application along with using the $location service to programmatically change the URL and navigate to a different route.

Q24. What is a $location service? Define its importance in AngularJS.

The URL of an application built in Angular can be tracked by employing a built-in service known as $location. This allows the maintenance of the URL, parsing it, and providing value to the controller. This helps to make modifications as if the value in $location is changed, and then the address bar will adjust accordingly and vice versa.

The $location service is important in AngularJS for several reasons:

• The $location service allows us to programmatically change the URL in the browser's address bar, including the path, search parameters, and hash fragment.
• The $location service is closely integrated with AngularJS routing (using the $routeProvider service) to provide a way to navigate between different views and states in your application by changing the URL based on the current route.
• The $location service provides methods for accessing various parts of the URL, such as the path, search parameters, and hash fragment.
• The $location service allows you to register event listeners to be notified when the URL changes.

Q25. What is ng-include? Define its use.

The ng-include directive is used for embedding purposes. This directive is used whenever one HTML page needs to be embedded within another. For instance:

<div ng-app = "" ng-controller = "Sample">

<div ng-include = "'samplefile.htm'"></div>

<div ng-include = "'examplefile.htm'"></div>

</div>

In the above example, the custom code embeds examplefile.htm and samplefile.htm within the AngularJS page.

Q24. What are the functions of filters in AngularJS?

Filters are a powerful feature that allows us to format and transform data displayed to the user in templates. They can be used in conjunction with expressions in templates, controllers, or services to modify the presentation of data before it is rendered to the user.

Some major function of filters include:

• Formatting Data: Filters can be used to format data for display purposes. For example, the currency filter can be used to format a number as a currency value based on the current locale.
• Filtering Arrays: Filters can be used to filter arrays based on specific criteria. For example, the filter filter can be used to create a new array containing only the items that match a given predicate.
• Sorting Arrays: Filters can be used to sort arrays based on specific criteria. For example, the orderBy filter can be used to sort an array of objects based on a specified property.
• Limiting Results: Filters can be used to limit the number of results displayed. For example, the limitTo filter can be used to limit an array to a specified number of items.
• Custom Filters: AngularJS allows us to define custom filters to perform specific formatting or transformation tasks that are not covered by the built-in filters.

Q26. Define the digest phase in AngularJS.

The digest phase is the last step in AngularJS’ data binding lifecycle. It runs an $evalAsync loop to detect any changes made to scope objects and then applies those changes to all of its child scopes and propagates them up through parent scopes until it has reached the root scope. During this process, several functions may be fired off, like watchers or directives (such as ng-show / ng-hide), which cause further UI updates–essentially ensuring everything stays synchronized.

Q27. What are the different phases of the lifecycle of AngularJS Scope?

The lifecycle of a scope involves several phases that describe its creation, mutation, and destruction.

• Creation: During the creation phase, a new scope is created either implicitly when a new controller is instantiated, or explicitly using directives like ng-controller or ng-repeat. The new scope inherits properties from its parent scope, creating a hierarchy of scopes.
• Watcher Registration: After the scope is created, AngularJS registers watchers on the scope to track changes to the model data. Watchers are functions that are invoked whenever the value of a watched expression changes. They are responsible for updating the view when the model changes and for propagating changes from the view back to the model.
• Model Mutation: During the model mutation phase, changes are made to the model data either by user interaction in the view or programmatically in the controller.
• Mutation Observation: AngularJS observes changes to the model and triggers the digest cycle to update the view when necessary. The digest cycle is the mechanism by which AngularJS detects changes to the model and updates the view to reflect those changes. It is triggered automatically by AngularJS, but can also be triggered manually if needed.
• Scope Destruction: When a scope is no longer needed, either because the associated controller or directive is destroyed or because it is no longer in use, AngularJS destroys the scope.

Q28. How will the application's performance be enhanced?

The developers of AngularJS have suggested the two methods listed below for improving performance in a real-world setting. The custom code is as follows:

Enable strict DI mode: Utilizing the ngStrictDi directive, the following may be done to achieve this goal:

<html ng-app="myFirstPageBuilt" ng-strict-di>

Disabling debug data: The debug info enabled function of the $compileProvider service may be used to do this, as demonstrated below:

app.config(function ($compileProvider) {

$compileProvider.debugInfoEnabled(false);

});

Along with the first two suggestions, the following advice will also help us perform better:

1. The one-way binding should be used wherever possible.
2. By forcing the applyAsync capability of $httpProvider to be used. Only generate a lot of $watches with a need because doing so will slow down the process by making the digest cycle longer.
3. The $cacheFactory directive may be used to save data to prevent recalculations when repeated computations involve the same type of data.
4. Pagination or endless scrolling can load fewer data if many items need to be looped rather than loading everything at once. The ng-InfiniteScroll directive in AngularJS is employed to enable infinite scrolling capacity.

Q29. How does animation work in Angular, and what are the different ways to animate elements in an Angular application?

Animation can be achieved using the @angular/animations module, which provides a powerful way to create complex animations for various elements and components in an application. Here's an overview of how animation works in Angular:

• Setting up Animations: To use animations in an Angular application, you need to import the BrowserAnimationsModule or NoopAnimationsModule module in your root module (e.g., AppModule) to enable support for animations. The BrowserAnimationsModule module is used to enable animations in the browser, while NoopAnimationsModule is a noop implementation that disables animations for testing purposes or when animations are not needed.
• Angular animations are defined using the trigger, state, style, transition, and animate functions provided by the @angular/animations module. The trigger function is used to define an animation trigger that can be associated with an element or component. Inside the trigger, we can define different states (state), styles (style), transitions (transition), and animations (animate) to control how the element or component should be animated based on different conditions or events.
• Once an animation trigger is defined, it can be applied to an element or component using the [@triggerName] syntax in the template.

Q30. What is Custom Directive? How can you create custom directives?

A directive defined by a user in AngularJS is called a "custom directive." It allows the user to extend the functionality of HTML by declaring desired functions. The following elements allow the creation of custom directives in AngularJS.

• Attribute
• CSS
• Element Directives

In AngularJS, custom directives are used to increase HTML's capabilities. Custom directives are defined using the "directive" function. A custom directive only swaps out the element it gets enabled for. The link() function of the custom directive is then used to process the element depending on the directive's scope when the AngularJS application has found the matching elements during bootstrap.

There are several in-built directives within AngularJS. First, we must create a directive called ttClass. Then we will follow the following steps.

1. We will save the file under the name tt-class.directives.ts.

2. We will import all the required libraries by using the following code.

import {Input, ElementRef, Directive, OnInit } from '@angular/core'

3. Then we will have to decorate the class using @directive and choose a selector. The name of the directive will be ttClassDirective. Let us consider the following code for doing so:

@Directive(

{ selector: '[ttClass]', } // ttClass is our selector

)

Export class ttClassDirective implements OnInit {

4. At this stage, our class will require an input, which will be used to retrieve a name from the parent Angular component.

@Input() ttClass: String;

5. Then the parent element will be attached as an attribute directive.

Constructor (private el: ElementRef) { } // Here, ElementRef acts like a wrapper for the parent DOM.

6. Then, a class will be added to the element using the following code.

ngOnInit ()

{ this.el.nativeElement.classList.add(this.ttClass); }

7. Finally, the complete code snippet for the custom directive will look as follows:

@Directive(

{ selector: '[ttClass]', } // ttClass is our selector

)

Export class ttClassDirective implements OnInit {

@Input() ttClass: String;

constructor (private el: ElementRef) { }

ngOnInit ()

{ this.el.nativeElement.classList.add(this.ttClass); }

Q31. What is Angular Singleton Service?

In Angular, a singleton service is a type of service that is instantiated only once during the lifetime of an application and is shared across various components and modules. When a service is marked as a singleton, Angular ensures that a single instance of that service is created and used throughout the entire application.

This design pattern is beneficial when you want to maintain a single, shared state or functionality that needs to be accessible globally. By using a singleton service, you can centralize the management of certain resources, data, or business logic, making it easier to maintain consistency and avoid redundant instances.

To create a singleton service in Angular, you typically provide it at the root level or within a module's providers array using the providedIn property. This ensures that the service is available for injection across the entire application.

Q32. Define AngularJS Models.

In an MVC-based application, the model is often in charge of modeling the data utilized in the view and managing user interactions, such as clicking buttons, scrolling, or creating other changes in the display. The $scope object is used as the most straightforward AngularJS implementations model.

However, the controller might be added to the scope with a provided name and effectively utilized as the model by using the controller method. In the latter instance, the object containing the information and procedures thought to comprise the model served as the controller. However, the controller was still linked to the $scope, which made configuring binding to the controller object simpler.

Q33. What are pipe characters in AngularJS?

The output in Angular JS is transformed via Angular Pipes. They act as data "makeup rooms," changing the information into a more appealing form. They do not modify the data; instead, they affect how the user sees them. Stops are specific functions created to take an input value, process it, and output the changed result. Numerous pipes are available in Angular. But you may also design lines specifically for your needs. Important characteristics include:

• In AngularJS, the pipe "|" symbol helps in defining lines.
• Pipes have the property of linking together through chains.
• The Colon (:) sign helps to pass pipes in arguments.

Q34. What is the ng-controller directive in AngularJS?

The ng-controller directive is used to attach a controller to a portion of the HTML document, known as a view. The controller is responsible for providing the behavior and state for that portion of the view. When the ng-controller directive is used, AngularJS creates a new instance of the specified controller and associates it with the HTML element on which the directive is applied.

Q35. Define Factory Method in AngularJS.

AngularJS Factory Method is an Angular service that allows you to create custom functions and objects. It can abstract complex logic, compute data or inject dependencies into your application. Factory methods are part of the ‘Service’ layer in Angular, which provides a singleton instance that can be accessed from anywhere in your app (similar to a private variable). A factory method takes two parameters: an array of arguments for injection and a function that will return the object/value created by this factory method call.

In real life, a scenario factory often serves as a class or container for functions that meet various application requirements. When used in conjunction with a function Object() { [native code] } function, it may be started in multiple controllers.

Syntax:

Module.factory(‘factory name’, function(){ Code });

Q36. How to use $ Scope and $rootscope in AngularJS?

The $Scope object gets used as an argument whenever a controller is made in AngularJS. AngularJS creates and injects a unique and different $Scope object into every controller in an application. As a result, a controller's $ Scope attached data and methods cannot be accessible by a controller's other methods.

The child controller will acquire the parent controller's scope object within the nested controller. As a result, the child controller can access properties that the parent controller has added, but the parent controller cannot access child controller-annexed properties.

The HTML element with the ng-app directive, which is present in all apps, provides the basis for creating the root scope. The entire program has access to the root scope. The property and values assigned with "$rootscope" are globally accessible to all controllers, meaning they may be used anywhere.

Q37. What is dependency injection in Angular JS?

Dependency injection (DI) in AngularJS is a software design pattern and a core concept that allows components of an application to be loosely coupled and easily testable. In the context of AngularJS, dependency injection refers to the mechanism by which objects (services, controllers, directives, etc.) declare their dependencies, and those dependencies are automatically provided to them by the AngularJS injector.

Let's see  how dependency injection works in AngularJS:

• Declaration of Dependencies: When defining a component (such as a service, controller, or directive) in AngularJS, you can declare its dependencies by specifying them as parameters in the component's constructor function or factory function.
• Injection of Dependencies: When an instance of the component is created by AngularJS (e.g., when the component is used in a module or another component), AngularJS's injector automatically resolves and injects the dependencies into the component based on the parameter names.
• Loose Coupling: By using dependency injection, components do not need to create or manage their dependencies explicitly. Instead, they rely on the injector to provide the necessary dependencies, which promotes loose coupling between components.
• Configuration and Reusability: Dependency injection allows for the configuration of dependencies at a central location (e.g., AngularJS modules), making it easy to swap dependencies or configure different sets of dependencies for different parts of the application.
• Testability: Dependency injection makes components easier to test, as dependencies can be easily mocked or replaced with stubs during unit testing. This allows for more isolated and focused tests without the need for complex setup or teardown logic.

Q38. How are Angular Expressions defined?

Expressions are JavaScript-like code snippets that are usually placed within double curly braces ({{}}) in the HTML templates. These expressions are evaluated by AngularJS within the context of the current scope, and their results are used to dynamically update the view.

Angular expressions can contain literals, operators, variables, and AngularJS-specific constructs. Some example of angular expressions includes:

• Literals: Numeric literals (123, 3.14), string literals ('Hello', "World"), boolean literals (true, false), object literals ({ prop: value }), array literals ([1, 2, 3]).
• Operators: Arithmetic operators (+, -, *, /), comparison operators (==, !=, <, >, <=, >=), logical operators (&&, ||, !), etc.
• Variables: Variables defined in the current scope, such as properties of the $scope object in a controller.
• AngularJS-specific Constructs: AngularJS provides additional constructs that can be used in expressions, such as filters ({{ expression | filter }}), directives (ng-show, ng-hide, etc.), and services (accessed through the $injector).

Q39. What are Angular Services? What is Log Service in AngularJS?

Services are objects or functions that are responsible for encapsulating specific, reusable functionality and providing it to other parts of an application. Services are used to organize and share code across an AngularJS application and are often used for tasks such as data manipulation, communication with servers, logging, authentication, and more.

AngularJS provides several built-in services, such as $http for making HTTP requests, $timeout for asynchronous operations, $location for URL manipulation, and many others. Additionally, developers can create custom services to encapsulate application-specific logic and functionality.

A log service in AngularJS is a custom service that is responsible for logging messages or events within an AngularJS application. It can be used to centralize logging functionality, making it easier to manage and customize the logging behavior across the application. 

A typical log service in AngularJS might include methods for logging messages at different levels of severity (e.g., debug, info, warn, error), formatting the log messages, and possibly sending the logs to a remote server for monitoring and analysis.

Q40. Explain what is the link function in AngularJS?

In AngularJS, the link function is a core part of the directive definition object (DDO) and is used to interact with the DOM (Document Object Model) and scope of a directive. When a directive is compiled and linked to the scope, the link function is executed to perform DOM manipulation, set up event listeners, and establish the directive's behavior. 

The link function has the following signature: 

function link(scope, element, attrs, ctrl) {
// DOM manipulation and directive logic here
}

Q41. Define DOM Events. What is DOM transformation in AngularJS?

DOM Events are the functional implications of a directive that give behavior to the elements of the DOM. Some common DOM events include:

Click: Occurs when a mouse button is clicked.
Mouseover: Occurs when the mouse pointer is moved over an element.
Keydown: Occurs when a key is pressed down.
Submit: Occurs when a form is submitted.
Load: Occurs when a resource (such as an image or script) has finished loading.

The directives are used to define the behavior of the objects within the application. Hence, these directives can be used to modify or change the object's and its children's behavior, which is regarded as a DOM transformation.

Q42. What does AngularJS's controller function do?

In AngularJS, the controller function is used to define a controller in an application module. Controllers are a fundamental part of AngularJS's MVC (Model-View-Controller) architecture and are responsible for defining the behavior and state of a view.

When we define a controller using the controller function, we are essentially creating a new constructor function that will be used to instantiate the controller. This constructor function is then associated with a particular view in the application, allowing us to define the logic and behavior that will be applied to that view.

Q43. What is ng-Hide Directive?

The ng-hide directive in AngularJS is used to conditionally hide or show HTML elements based on an expression. When the expression provided to ng-hide evaluates to true, the associated HTML element is hidden by applying the display: none; CSS style to it. Conversely, when the expression evaluates to false, the element is displayed normally.

Q44. Discuss the applications of compile function in AngularJS.

The compile function is a core part of the directive definition object (DDO) and is used to manipulate the DOM before it is linked to the scope. The compile function is optional, and not all directives need to have it. However, when used, the compile function provides a way to perform advanced DOM manipulation and customization based on the directive's configuration and the application's state.

Some key applications of the compile function includes:

• Template Manipulation: The compile function allows you to modify the directive's template before it is linked to the scope. 
• DOM Transformation: We can use the compile function to transform the DOM structure based on the directive's requirements.
• Access to Directives: Inside the compile function, we have access to the directive's attributes, controller, and transcluded content.
• Pre-linking Setup: The compile function is executed before the link function, allowing you to set up the directive's environment before it is linked to the scope.

Q45. How does AngularJS uses $ and $$ as prefixes?

The $ and $$ prefixes are used to denote variables and methods that are part of the AngularJS framework itself. These prefixes are a convention used by the AngularJS core developers to distinguish built-in properties and methods from user-defined properties and methods.

• $ Prefix: Variables and methods with a $ prefix are considered public API elements of AngularJS. These elements are intended to be used by developers when working with AngularJS's public API.Examples of commonly used $-prefixed elements include $scope, $http, $rootScope, $q (for promises), $timeout, etc.
• $$ Prefix: Variables and methods with a $$ prefix are considered private or internal implementation details of AngularJS. These elements are not intended to be used directly by developers, as they are subject to change in future versions of AngularJS. Examples of commonly used $$-prefixed elements include $$watchers, $$listeners, $$phase, $$postDigest, etc.

Q46. What are the factory functions in AngularJS?

Factory functions are a type of function used to define factories for creating instances of AngularJS services. AngularJS services are objects or functions that provide specific functionality and can be injected into other parts of an application, such as controllers, directives, or other services.

A factory function in AngularJS is responsible for creating and configuring instances of a service. It returns an object or a function that represents the service and can be injected into other components. Factory functions are often used when we need more control over the creation and initialization of a service instance compared to using a simple value or a constructor function.

Q47. What is a constructor function in AngularJS?

A constructor function is a type of function used to define a constructor for a custom AngularJS service. AngularJS services are objects or functions that are designed to carry out specific tasks, such as data manipulation, communication with servers, or providing shared functionality across different parts of an application.

When we define a constructor function for an AngularJS service, we are essentially defining a blueprint for creating instances of that service. This allows us to define the behavior and properties of the service, as well as any dependencies it may have on other services or components within the AngularJS application.

Q48. Explain what is Ng-Disabled Directive.

The ng-disabled directive in AngularJS is used to dynamically disable or enable HTML elements based on an expression. When the expression provided to ng-disabled evaluates to true, the associated HTML element is disabled, preventing user interaction with it. Conversely, when the expression evaluates to false, the element is enabled, allowing user interaction.

Q49. What are AngularJS expressions?

AngularJS expressions are code snippets usually placed in binding such as {{ expression }} and allow us to insert dynamic values into our HTML. They can contain literals, operators, and variables, which AngularJS executes at runtime. Expressions are similar to JavaScript but don’t have access to any global objects like windows or documents, whereas, in JavaScript, these global objects would always be present automatically.

We can bind data from the model (scope) within a specified context by writing an expression. The upshot is that properties of several different models all get updated whenever user input changes with minimal effort required on your part thanks to two-way data binding made possible by angular's magic behind the scenes!

Q50. Explain the Hierarchical structure of AngularJS.

As we know, Angular JS is a structural framework for creating dynamic web applications. It uses an MVC (Model-View-Controller) architecture, which divides the application into three components: model, view, and controller. The hierarchical structure of AngularJS can be explained as follows:

1. Modules- You will find modules at the top level of your application. These containers house several pieces of code the application needs, such as controllers, directives, filters, and services.
2. Controllers- They provide programmatic control to specific sections or views within your app. They also contain functions mapped with variables associated with HTML elements on a page, allowing them to take user data and manipulate it according to other programming logic before displaying it on screen.
3. Services- A service acts like any external resource providing additional functionality to your app without its own UI element/view.
4. Directives- They allow developers to create custom HTML tags as markers when linking different parts of our JavaScript codebase.
5. Filters- Filters are primarily used for formatting data within the view layer of your app. They allow us to perform various types of operations like sorting, capitalizing strings, converting numbers into currency, etc.

Q51. Explain the Scope Model of AngularJS.

The Scope Model of AngularJS is the mechanism by which data and logic are brought together within a web application. It bridges the presentation layer (view) and the business logic that resides in controllers. In other words, it provides access to models from templates (HTML view), binds events back into controller functions for manipulation, permits communication with services such as AJAX requests, etc. And finally, it serves up context-specific operations through filters for formatting or manipulating data before being presented onscreen.

Every Angular app contains one root scope with multiple child scopes created from various directives like ng-repeat or ng-switch, which may further encapsulate related code. These child scopes provide ways to bubble messages up/down to parent siblings depending upon certain conditions.

Q52. Explain the directive scopes.

Directives can have their own scopes, which define the context in which the directive's template and behavior operate. Understanding directive scopes is crucial for building reusable and encapsulated components in AngularJS applications. 

• By default, directives in AngularJS use the scope inherited from their parent controller or directive. This means that they share the same scope as their parent unless a new scope is explicitly created for the directive. 
• Directives can have an isolated scope, which is not inherited from the parent scope. An isolated scope is useful for creating reusable components that encapsulate their own data and behavior without relying on the parent scope. An isolated scope can be created by specifying the scope property in the directive's definition object, using one of the following options: 
  scope: false (default): Inherit the parent scope.
  scope: true: Create a new child scope that prototypically inherits from the parent scope.
  scope: { ... }: Create an isolated scope with specific properties defined by an object literal.
• Directives can have their own controller, which is responsible for defining the directive's behavior and handling interactions within the directive's scope. Controllers can be defined using the controller property in the directive's definition object, allowing you to encapsulate directive-specific logic.

Q53. Explain what is Ng-Bind Directive.

The ng-bind directive is used to bind the content of an HTML element to a model property. It updates the content of the HTML element whenever the associated model property changes, ensuring that the view reflects the latest data from the model. The ng-bind directive is particularly useful for displaying dynamic content in the UI based on changes in the underlying data.

• Syntax: The ng-bind directive is typically used as an attribute on an HTML element, specifying the model property whose value should be bound to the element's content.

     <div ng-bind="expression"></div>

• Data Binding: When the page is loaded or the model is updated, AngularJS evaluates the expression provided to ng-bind and sets the content of the associated HTML element to the result of the expression. If the expression is a model property, the content of the HTML element will be updated whenever the value of the model property changes, ensuring that the view reflects the latest data.
• Security Considerations: Another benefit of using ng-bind is that it helps prevent potential security vulnerabilities such as Cross-Site Scripting (XSS) attacks by automatically escaping any potentially dangerous content before it is rendered in the UI.

Q54. Explain what is Ng-Bind-HTML Directive.

The ng-bind directive in AngularJS is used to bind the content of an HTML element to a model property. It updates the content of the HTML element whenever the associated model property changes, ensuring that the view reflects the latest data from the model. The ng-bind directive is particularly useful for displaying dynamic content in the UI based on changes in the underlying data.

• Syntax: The ng-bind-html directive is typically used as an attribute on an HTML element, specifying the model property whose value contains the HTML content to be rendered.
  

  <div ng-bind-html="expression"></div>

• Sanitization: Because ng-bind-html renders HTML content, AngularJS automatically sanitizes the content to prevent Cross-Site Scripting (XSS) attacks and other security vulnerabilities.
• Trusted Content: If the HTML content is known to be safe and trusted (e.g., it comes from a trusted source), you can use the $sce.trustAsHtml() method to mark the content as trusted and bypass the sanitization process. However, this should be done with caution to avoid security risks.

Q55. Explain what is Ng-Show Directive

The ng-show directive in AngularJS is used to conditionally display or hide an HTML element based on an expression. When the expression associated with ng-show evaluates to true, the element is displayed; otherwise, it is hidden. This directive is particularly useful for dynamically showing or hiding elements based on the state of the application or certain conditions.

• Syntax: The ng-show directive is typically used as an attribute on an HTML element, specifying an expression that determines whether the element should be shown or hidden.
  

  <div ng-show="expression"></div>

• Dynamic Visibility: The ng-show directive dynamically adds or removes the ng-hide CSS class to the element based on the evaluation of the expression. When the expression is true, the ng-hide class is removed, and the element becomes visible according to its default styling or any additional CSS applied to it.
• Use Cases: ng-show is commonly used to conditionally display elements based on various factors such as the state of a variable, the result of a function, user permissions, etc.

Q56. What is one-way data binding in Angular JS?

One-way data binding in AngularJS is a data flow mechanism where the data is transferred from the model (JavaScript objects defined in the application) to the view (HTML templates), but not the other way around. In one-way data binding, changes in the model update the view automatically, but changes in the view do not update the model automatically. 

Model to View: When the application's model changes (e.g., due to user interaction or other events), AngularJS automatically updates the corresponding parts of the view to reflect these changes.

View to Model: Unlike two-way data binding, in one-way data binding, changes made in the view (e.g., user input in form fields) do not automatically update the model.

One-way data binding creates a unidirectional flow of data from the model to the view, which simplifies the data flow and makes it easier to reason about how data is displayed and updated in the application.

Q57. What are the Scope Model Values in AngularJS?

The scope model values refer to the data and properties that are bound to the scope object in the application. The scope model represents the state of the application and is used to store and manage data that is used by the views (HTML templates) and controllers.

Some key points about scope model values includes:

• Data Binding: Scope model values are used for two-way data binding between the view and the controller. Changes to the model in the controller automatically update the view, and changes in the view update the model.
• Scope Hierarchy: AngularJS uses a hierarchical scope system where each controller creates its own scope, which inherits from its parent scope. This allows for the organization of data and logic into smaller, manageable scopes.
• Scope Properties: Scope model values are defined as properties of the scope object. These properties can be simple values (strings, numbers, booleans), objects, arrays, functions, or even references to services.
• Accessing Scope Model Values: In controllers, scope model values can be accessed and manipulated directly by using the $scope object. For example:
  app.controller('MyController', function($scope) {
  $scope.message = 'Hello, World!';
  });
• Binding in Views: In views (HTML templates), scope model values are accessed using expressions like {{ expression }} or directives like ng-model, ng-bind, etc. For example:
  <div>{{ message }}</div>
• Events and Watches: Scope model values can be watched for changes using the $watch function, allowing for reactive behavior in response to changes in the model. Additionally, events can be broadcasted and emitted within the scope hierarchy using $broadcast and $emit.

Q58. What are the custom filters in AngularJS and how they are created?

Custom filters allows us to create their own filters for formatting and transforming data displayed in the UI. Custom filters can be used to manipulate the output of expressions in templates, providing a way to customize how data is presented to users. 

To create custom filters: 

• Define the Filter Function: To create a custom filter, we define a JavaScript function that takes input data and optional parameters and returns the filtered output. The filter function should be registered with AngularJS using the filter() method of the module. For example:

angular.module('myApp', [])
.filter('customFilter', function() {
return function(input, param1, param2) {
// Filter logic goes here
return filteredOutput;
};
});

• Use the Custom Filter in Templates: Once the custom filter is defined, we can use it in AngularJS templates by using the pipe (|) syntax followed by the filter name. For example:
  <div>{{ data | customFilter:param1:param2 }}</div>
• Inject the Filter into Controllers or Services: If we need to use the custom filter in JavaScript code (e.g., controllers, services), we can inject it as a dependency and use it like any other function.

For example:

angular.module('myApp')
.controller('MyController', function($scope, customFilterFilter) {
$scope.filteredData = customFilterFilter(data, param1, param2);
});

Optional Parameters: Custom filters can accept optional parameters that are passed after the filter name in the template. These parameters can be used to customize the behavior of the filter based on specific requirements.

Q59. Explain the different styles of API in AngularJS.

In AngularJS, we have different styles of APIs that can be used to interact with the framework and build applications. Some of them being:

• Directive Definition Object (DDO): The Directive Definition Object (DDO) is a common style used to define custom directives in AngularJS. It involves creating a JavaScript object that contains various configuration options and functions for the directive, such as restrict, template, link, controller, scope, etc.
• Module API: The Module API is used to create and configure AngularJS modules, which are containers for different parts of an application such as controllers, services, directives, filters, etc.
• Service API: The Service API is used to define and register services in AngularJS, which are reusable components that encapsulate business logic or functionality.
• Scope API: The Scope API is used to interact with AngularJS scopes, which are objects that provide a context for evaluating expressions and one-time binding data between the view and the controller.
• Route API: The Route API is used to define and configure routing in AngularJS applications, allowing developers to create single-page applications (SPAs) with different views and navigation.
• Filter API: The Filter API is used to define and register filters in AngularJS, which are used to format and transform data in templates. 

Q60. Explain the DOM structure in AngularJS.

In AngularJS, the Document Object Model (DOM) structure plays a crucial role in defining the structure of the application's user interface (UI) and how it interacts with the underlying data and logic. The DOM structure  is dynamic and is primarily defined by the HTML templates, directives, controllers, and data binding expressions used in the application.

The key components of the DOM structure in AngularJS are:

• HTML Templates: AngularJS applications are built using HTML templates that define the structure of the UI. These templates can contain standard HTML elements as well as AngularJS-specific directives and expressions.
• Directives: Directives are markers on a DOM element that tells HTML compiler ($compile) to attach a specified behavior to that DOM element or even transform the DOM element and its children.
• Controllers: Controllers are JavaScript functions that are responsible for providing the behavior and data for a particular section of the UI.
• Data Binding: Data binding is a core feature of AngularJS that establishes a connection between the application's data (in the model) and the UI elements (in the view).
• Scope: Scopes are JavaScript objects that serve as the context for evaluating expressions. They are used to provide a context for data binding and to organize the data and behavior of the application.
• Services: Services are singleton objects that are used to encapsulate shared business logic, data, or functionality that can be used across different parts of an application.

Q61. Is it possible to assign a value to an Angular variable using a PHP session variable without making an HTTP request?

No, it's not possible to directly assign a value to an Angular object variable using a PHP session variable without making an HTTP request. AngularJS runs on the client-side (in the user's browser), while PHP runs on the server-side. PHP session variables are stored on the server and are not directly accessible to AngularJS without some form of server-side interaction, such as an HTTP request.

To use PHP session variables in an AngularJS application, you typically need to make an HTTP request from the client-side (AngularJS) to the server-side (PHP) to retrieve the session variable's value. This can be done using AJAX or by embedding the session variable's value in the initial HTML page generated by PHP.

Q62. Explain the auto bootstrap process in AngularJS?

The auto-bootstrap process refers to the automatic initialization of an AngularJS application when the web page containing the application is loaded by the browser. This process is driven by the ng-app directive, which is used to declare the root element of the AngularJS application within the HTML document.

• To enable auto-bootstrapping, we include the ng-app directive in the HTML markup of our web page, typically on the root element of our application. 
  <html ng-app="myApp">
  <!-- ... -->
  </html>
• When the browser loads the HTML document, it encounters the ng-app directive, which triggers the AngularJS framework to bootstrap the application.
• AngularJS then starts the process of compiling the HTML and initializing the application's modules, controllers, services, directives, and other components based on the configuration provided in the application module (myApp in this example).
• AngularJS compiles the HTML DOM starting from the root element where ng-app was declared, traversing the DOM tree to identify any AngularJS directives or expressions.
• Once the compilation and linking process is complete, AngularJS starts executing the application by processing user interactions, updating the DOM based on model changes, and responding to events.

Q63. How can you maintain logs in AngularJS?

In AngularJS, we can maintain logs using various techniques and tools to track and manage application logs effectively. Some common ones are: 

• Console Logging: Using the console.log(), console.warn(), console.error(), etc., functions to log messages to the browser's console for debugging and monitoring purposes.
• Custom Logging Service: Create a custom logging service using AngularJS's factory or service methods to encapsulate logging functionality. This service can provide methods for logging messages at different levels (e.g., info, debug, warning, error) and can be injected into various parts of the application where logging is needed.
• Third-Party Logging Libraries: Utilizing third-party logging libraries such as Log4js, Winston, or Bunyan, which provide more advanced logging features like log levels, log formatting, log storage, and more.
• Server-Side Logging: Implement server-side logging by sending log messages from the client-side application to the server using HTTP requests. On the server-side, log messages can be stored in files, databases, or other logging systems for long-term storage and analysis.

Q64. What are some of the most common API functions in AngularJS?

In AngularJS, we have several common API functions that are frequently used to interact with the framework and build dynamic web applications. Some of them are discussed below:

• angular.module(name, [requires], [configFn]): Used to create or retrieve a module.
• module.conname,troller( constructor): Registers a controller with the module.
• $scope.$watch(watchExpression, listener, [objectEquality]): Registers a watch function to be called when the watchExpression changes.
• $scope.$apply([exp]): Processes the exp expression and its children using the $digest cycle.
• module.directive(name, directiveFactory): Registers a new directive with the module.
• compile(tElement, tAttrs, transclude): Compiles a piece of HTML and returns a linking function.
• module.service(name, constructor): Registers a new service with the module.
• $http.get(url, [config]): Sends an HTTP GET request to the specified URL.
• module.filter(name, filterFactory): Registers a new filter with the module.
• filter('filterName', filterFunction): Defines a custom filter function.
• module.config(configFn): Registers a configuration function to be called when the module is loaded.
• $routeProvider.when(path, route): Defines a new route and associates it with a template and controller.
• inject(function): Injects dependencies into a test function.
• module('moduleName'): Retrieves a reference to a module for testing purposes.

Q65. What is AOT Compilation? What are the advantages associated with it?

AOT (Ahead-of-Time) compilation refers to the process of compiling AngularJS templates and components during the build phase of the application, before it is deployed to the client's web browser. This is in contrast to JIT (Just-in-Time) compilation, where the compilation of templates and components occurs in the client's browser at runtime.

Advantages of AOT compilation in AngularJS include:

• Faster Initial Load Time: AOT-compiled applications tend to load faster because the templates and components are already compiled into JavaScript during the build process. This eliminates the need for the client's browser to perform compilation at runtime, resulting in faster initial rendering of the application.
• Optimized Performance: AOT compilation can lead to improved runtime performance as the generated JavaScript code is often more optimized compared to code generated by JIT compilation. This can result in better overall application performance, especially on low-powered devices or networks with limited bandwidth.
• Template Error Detection: AOT compilation can detect template errors, such as syntax errors or binding errors, during the build process. This can help catch and fix issues earlier in the development lifecycle, reducing the likelihood of runtime errors in the deployed application.
• Security: AOT compilation can improve the security of an AngularJS application by reducing the risk of client-side template injection attacks. Since templates are precompiled, there is no opportunity for malicious code to be injected and executed at runtime.
• Smaller Bundle Sizes: AOT compilation can lead to smaller bundle sizes for AngularJS applications. This is because the compiled code is optimized and tree-shaken during the build process, removing unused code and reducing the overall size of the application bundle.

Q66. How do we achieve internationalization?

In AngularJS, internationalization (i18n) can be achieved using the built-in $locale service, AngularJS filters, and external libraries like angular-translate. 

• AngularJS provides filters like currency, date, and number that can automatically format values based on the user's locale. These filters can be used in templates to display formatted content based on the user's language and region.
• For dynamic content that needs to be translated based on the user's locale, AngularJS services can be used to load and manage translation data.
• The $locale service in AngularJS provides access to locale-specific settings, such as date and number formats. We can use this service to customize the display of locale-specific data in your application.
• External libraries like angular-translate provide a more comprehensive solution for internationalization in AngularJS. These libraries offer features like dynamic language switching, translation loading from JSON files or APIs, and interpolation of translated strings.

Q67. Can we have two ng-app directives for a single Angular application?

No, it is not possible to have two ng-app directives for a single AngularJS application. The ng-app directive is used to define the root element of an AngularJS application, and there should only be one such directive in the HTML document. This directive tells AngularJS which part of the HTML document should be treated as the root of the application and where to start the compilation and linking process.

If we attempt to use multiple ng-app directives in a single document, AngularJS will throw an error, as it expects only one application root.

Q68. How do you reset a “$timeout”, and disable a “$watch()” in angularJS?

Resetting a $timeout: If we want to reset a $timeout before it is executed, we can use the cancel() method provided by the $timeout service. This method cancels the execution of the timeout and prevents its callback function from being invoked. 

// Store the reference to the timeout promise
var myTimeout = $timeout(function() {
// Timeout callback function
}, 1000);

// Later, if you want to reset the timeout
$timeout.cancel(myTimeout);

Disabling a $watch(): If we want to temporarily disable a $watch() expression from watching for changes, we can store the deregistration function returned by the $watch() method and then call it to disable the watcher. When we want to re-enable the watcher, we can simply re-register the $watch() expression.

// Create a watch expression and store the deregistration function
var deregisterWatch = $scope.$watch('myModel', function(newValue, oldValue) {
// Watcher function
});

// Later, if you want to disable the watcher
deregisterWatch();

Q69. Which means of communication between modules of your application are easily testable?

In AngularJS, the means of communication between modules that are easily testable are those that follow the principles of dependency injection and separation of concerns.

• Services are a common way for different parts of an AngularJS application to communicate. They are designed to encapsulate reusable functionality and can be injected into controllers, directives, and other services.
• AngularJS provides mechanisms for broadcasting and emitting events within the application using $broadcast and $emit. This allows different parts of the application to communicate without direct dependencies.
• Directives with isolated scopes can be used to encapsulate behavior and communicate with other parts of the application through attributes or events.
• AngularJS's dependency injection system allows components to declare their dependencies explicitly, making it easy to inject mock or stub dependencies for testing purposes.

Q70. What are DSL animation functions in AngularJS

In AngularJS, DSL (Domain-Specific Language) animation functions are a set of functions provided by the AngularJS framework to create animations declaratively. These functions allow developers to define animations using a high-level, expressive syntax that is tailored to the needs of web application animations.

Some common DSL animation functions include:

• $animate.addClass(element, className, options):

  Adds a CSS class to an element with optional animation options.

• $animate.removeClass(element, className, options):

  Removes a CSS class from an element with optional animation options.

• $animate.enter(element, parent, after, options):

  Inserts an element into the DOM relative to another element with optional animation options.

• $animate.leave(element, options):

  Removes an element from the DOM with optional animation options.

• $animate.move(element, parent, after, options):

  Moves an element within the DOM relative to another element with optional animation options.

• $animate.setClass(element, add, remove, options):

  Adds and removes CSS classes from an element with optional animation options.\

Q71. Can we make an ajax call using Angular JS? How?

Yes, we can make AJAX (Asynchronous JavaScript and XML) calls using AngularJS. AngularJS provides the $http service, which allows us to make HTTP requests to fetch data from a server or send data to a server.

Example:

// Inject the $http service into your controller
app.controller('MyController', function($scope, $http) {
// Define the URL for the HTTP GET request
var url = 'https://api.example.com/data';

// Make the HTTP GET request
$http.get(url)
.then(function(response) {
// Success callback function
$scope.data = response.data; // Assign the response data to a $scope variable
})
.catch(function(error) {
// Error callback function
console.error('Error fetching data:', error);
});
});

In this example:

• We inject the $http service into our controller.
• We define the URL for the HTTP GET request (URL).
• We use the $http.get() method to make the GET request to the specified URL.
• We use the .then() method to handle the successful response from the server. Inside the success callback function, we assign the response data to a $scope variable ($scope.data).
• We use the .catch() method to handle any errors that occur during the HTTP request.

Q72. Explain how AngularJS handles routing and how it differs from server-side routing.

In AngularJS, routing is used to manage the navigation and state of a single-page web application (SPA) by mapping URLs to different views or states within the application. AngularJS provides the $routeProvider service to define routes, which are then used to configure the application's navigation behavior.

AngularJS performs client-side routing, which means that routing is handled entirely within the browser without requiring a round-trip to the server for each navigation change. When a user clicks on a link or performs an action that changes the URL, AngularJS intercepts the URL change and updates the view based on the corresponding route configuration.

Route definitions in AngularJS are configured using the $routeProvider service, which allows you to define routes based on URL patterns and map them to specific controllers and templates. Each route definition typically includes a URL pattern, a controller, and a template or templateUrl. When a route is matched, AngularJS renders the associated view by replacing the content of a designated HTML element (usually a div with an ng-view directive) with the contents of the template associated with the route.

Server-side routing, commonly used in traditional extensible web applications, involves the server responding to each URL request with a full HTML page, often generated dynamically based on the requested URL. In contrast, AngularJS handles routing on the client side, allowing for faster navigation and a more responsive user interface without the need for full page reloads.

Q73. Explain the concept of promises in AngularJS and how they are used for asynchronous operations.

Promises are a way to handle asynchronous operations. They represent a value that may not be available yet but will be resolved in the future, either successfully with a value or unsuccessfully with an error. Promises provide a standardized way to write asynchronous code in a more readable and manageable manner. They are commonly used for tasks like HTTP requests or any operation that needs to wait for a result. AngularJS provides the $q service to work with promises, allowing us to create, manipulate, and handle them easily. Promises can be chained together using the then() method, and errors can be handled using the catch() method. Overall, promises are a key feature in AngularJS for managing asynchronous operations.

Q74. What are AngularJS decorators, and how are they used to modify services, directives, and controllers?

Decorators are a powerful feature that allows us to modify or extend the behavior of services, directives, and controllers provided by AngularJS or third-party libraries. Decorators are functions that wrap or enhance the functionality of existing components without modifying their original source code. 

We can use decorators to modify the behavior of AngularJS services by intercepting the original service and adding additional functionality. Decorators for services are created using the $provide.decorator() method, which takes the name of the service and a function that returns the modified service. Inside the decorator function, you can access the original service and modify its behavior by adding new methods, properties, or modifying existing ones.

Decorators for directives are created using the $compileProvider.decorator() method, which takes the name of the directive and a function that returns the modified directive definition object. Inside the decorator function, you can modify the directive's compile or link functions, change its template or template URL, or add new functionality.

While controllers in AngularJS are not typically modified using decorators, you can still use decorators to enhance controllers indirectly by modifying the services they depend on or by injecting additional dependencies into them.

Q75. Discuss the concept of transclusion in AngularJS directives and how it is used.

Transclusion is a powerful feature that allows us to create directives with flexible and reusable templates. Transclusion enables you to define a directive that wraps arbitrary content provided by the user and includes it in the directive's template. This is particularly useful when we want to create directives that can encapsulate complex UI components while still allowing users to customize the content within them.

Transclusion is achieved using the transclude property in the directive definition object. When transclude is set to true, AngularJS includes the content of the directive's element (and its children) in the directive's template, typically using the ng-transclude directive in the template.

app.directive('myDirective', function() {
return {
restrict: 'E',
transclude: true,
template: '<div>Directive Content: <ng-transclude></ng-transclude></div>'
};
}); 

In this example:

• We define a directive called myDirective using the app.directive() method.
• We set the restrict property to 'E' to indicate that this directive can be used as an element.
• We set transclude: true in the directive definition object to enable transclusion.
• We define a template for the directive that includes the ng-transclude directive, which tells AngularJS to include the content of the directive's element and its children at that position in the template.

Now, when you use the my-directive element in your HTML, any content inside the my-directive tags will be transcluded into the directive's template:

<my-directive>
<p>This content will be transcluded into the directive's template.</p>
</my-directive>

When the above HTML is rendered, the output will be:

<div>Directive Content: <p>This content will be transcluded into the directive's template.</p></div>

Facing an interview for AngularJS development is not an easy task. However, with the appropriate level of preparation, you can easily crack the interview. The key ingredient to any successful technical interview is to have a good grasp of the fundamentals and concepts. And one can prepare for the interview by learning the questions that have been mentioned in this blog.