Angular Interview Questions and Answers

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Why were client-side frameworks like Angular introduced?

Back in the day, web developers used VanillaJS and jQuery to develop dynamic websites but, as the logic of one’s website grew, the code became more and more tedious to maintain. For applications that use complex logic, developers had to put in extra effort to maintain separation of concerns for the app. Also, jQuery did not provide facilities for data handling across views.

For tackling the above problems, client-side frameworks like Angular came into the picture, which made life easier for the developers by handling separation of concerns and dividing code into smaller bits of information (In the case of Angular, called Components).

Client-side frameworks allow one to develop advanced web applications like Single-Page-Application. Not that we cannot develop SPAs using VanillaJS, but by doing so, the development process becomes slower.

Angular Interview Questions

What is an AOT compilation? What are its advantages?

The Ahead-of-time (AOT) compiler converts the Angular HTML and TypeScript code into JavaScript code during the build phase, i.e., before the browser downloads and runs the code.

Some of its advantages are as follows. 

  1. Faster rendering
  2. Fewer asynchronous requests
  3. Smaller Angular framework download size
  4. Quick detection of template errors
  5. Better security

Explain Dependency Injection?

Answer:  Dependency injection is an application design pattern that is implemented by Angular and forms the core concepts of Angular. 

Let us understand in a detailed manner. Dependencies in Angular are services which have a functionality. Various components and directives in an application can need these functionalities of the service. Angular provides a smooth mechanism by which these dependencies are injected into components and directives.

What are the key components of Angular?
Angular has the below key components,

Component: These are the basic building blocks of angular application to control HTML views.

Modules: An angular module is set of angular basic building blocks like component, directives, services etc. An application is divided into logical pieces and each piece of code is called as “module” which perform a single task.

Templates: This represent the views of an Angular application.

Services: It is used to create components which can be shared across the entire application.

Metadata: This can be used to add more data to an Angular class.

What is data binding? Which type of data binding does Angular deploy?

Data binding is a phenomenon that allows any internet user to manipulate Web page elements using a Web browser. It uses dynamic HTML and does not require complex scripting or programming. We use data binding in web pages that contain interactive components such as forms, calculators, tutorials, and games. Incremental display of a webpage makes data binding convenient when pages have an enormous amount of data. 

Angular uses the two-way binding. Any changes made to the user interface are reflected in the corresponding model state. Conversely, any changes in the model state are reflected in the UI state. This allows the framework to connect the DOM to the Model data via the controller. However, this approach affects performance since every change in the DOM has to be tracked. 

What do you mean by string interpolation?

String interpolation in Angular, also known as the mustache syntax, only allows one-way data binding. It is a special syntax that makes use of double curly braces {{}} so that it can display the component data. Inside the braces are the JavaScript expressions that Angular needs to execute to retrieve the result, which can further be inserted into the HTML code. Moreover, as part of the digest cycle, these expressions are regularly updated and stored.

What are the differences between Angular decorator and annotation?

In Angular, decorators are design patterns that help in the modification or decoration of the respective classes without making changes in the actual source code.

Annotations, on the other hand, are used in Angular to build an annotation array. They use the Reflective Metadata library and are a metadata set of the given class.

List out differences between AngularJS and Angular

Architecture

AngularJS uses MVC or Model-View-Controller architecture, where the Model contains the business logic, Controller processes information and View shows the information present in the Model.

Angular replaces controllers with Components. Components are nothing but directives with a predefined template.

Language

AngularJS uses JavaScript language, which is a dynamically typed language.

Angular uses TypeScript language, which is a statically typed language and is a superset of JavaScript. By using statically typed language, Angular provides better performance while developing larger applications.

Mobile Support

AngularJS does not provide mobile support.

Angular is supported by all popular mobile browsers.

Structure

While developing larger applications, the process of maintaining code becomes tedious in the case of AngularJS.

In the case of Angular, it is easier to maintain code for larger applications as it provides a better structure.

Expression Syntax

While developing an AngularJS application, a developer needs to remember the correct ng-directive for binding an event, or a property. Whereas in Angular, property binding is done using “[ ]” attribute and event binding is done using “( )” attribute.

What is the difference between pure and impure pipe?
A pure pipe is only called when Angular detects a change in the value or the parameters passed to a pipe. For example, any changes to a primitive input value (String, Number, Boolean, Symbol) or a changed object reference (Date, Array, Function, Object). An impure pipe is called for every change detection cycle no matter whether the value or parameters changes. i.e, An impure pipe is called often, as often as every keystroke or mouse-move.

What is the AOT (Ahead-Of-Time) Compilation? What are its advantages?

Answer:  An angular application consists of components and templates which a browser cannot understand. Therefore, every Angular application needs to be compiled before running inside the browser. The Angular compiler takes in the JS code, compiles it, and then produces some JS code. It is known as AOT compilation and happens only once per occasion per user. 

There are two kinds of compilation that Angular provides:

JIT(Just-in-Time) compilation: the application compiles inside the browser during runtime

AOT(Ahead-of-Time) compilation: the application compiles during the build time.

Advantages of AOT compilation:

  • Fast Rendering: The browser loads the executable code and renders it immediately as the application is compiled before running inside the browser. 
  • Fewer Ajax Requests: The compiler sends the external HTML and CSS files along with the application, eliminating AJAX requests for those source files. 
  • Minimizing Errors: Easy to detect and handle errors during the building phase. 
  • Better Security: Before an application runs inside the browser, the AOT compiler adds HTML and templates into the JS files, so there are no extra HTML files to be read, thus providing better security for the application.

What is dependency injection in Angular?
Dependency injection (DI), is an important application design pattern in which a class asks for dependencies from external sources rather than creating them itself. Angular comes with its own dependency injection framework for resolving dependencies( services or objects that a class needs to perform its function). So you can have your services depend on other services throughout your application.

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