Angular interview questions

1. What’s new in Angular 7?
Certain tools are optimized in the new version of Angular,
let us see what the tools are:
Angular 7 supports Typescript version 2.4
Angular 7 supports RxJS which has new features like
Pipeable Operators
A build tool to make the js bundles (files) lighter
Ahead of Time (AOT) is updated to be on by default
Events like ActivationStart and ActivationEnd are
introduced in Router

Name the building blocks of
Angular.
The Angular application is made using the following:
Modules
Component
Template
Directives
Data Binding
Services
Dependency Injection
Routing

Components – A component controls one or more views. Each view
is some specific section of the screen. Every Angular application has
at least one component, known as the root component. It is
bootstrapped inside the main module, known as the root module. A
component contains application logic defined inside a class. This
class is responsible for interacting with the view via an API of
properties and methods.
Data Binding – The mechanism by which parts of a template
coordinates with parts of a component is known as data binding. In
order to let Angular know how to connect both sides (template and
its component), the binding markup is added to the template HTML.
Dependency Injection (DI) – Angular makes use of DI to provide
required dependencies to new components. Typically, dependencies
required by a component are services. A component’s constructor
parameters tell Angular about the services that a component
requires. So, a dependency injection offers a way to supply fully-
formed dependencies required by a new instance of a class.

Directives – The templates used by Angular are dynamic in nature. Directives are
responsible for instructing Angular about how to transform the DOM when rendering a
template. Actually, components are directives with a template. Other types of directives
are attribute and structural directives.
Metadata – In order to let Angular know how to process a class, metadata is attached to
the class. For doing so decorators are used.
Modules – Also known as NgModules, a module is an organized block of code with a
specific set of capabilities. It has a specific application domain or a workflow. Like
components, any Angular application has at least one module. This is known as the root
module. Typically, an Angular application has several modules.
Routing – An Angular router is responsible for interpreting a browser URL as an instruction
to navigate to a client-generated view. The router is bound to links on a page to tell
Angular to navigate the application view when a user clicks on it.
Services – A very broad category, a service can be anything ranging from a value and
function to a feature that is required by an Angular app. Technically, a service is a class
with a well-defined purpose.
Template – Each component’s view is associated with its companion template. A template
in Angular is a form of HTML tags that lets Angular know that how it is meant to render
the component.

3. What is Transpiling in Angular?
Transpiling is the process of converting the
typescript into javascript. Though typescript is
used to write code in the Angular
applications, the code is internally transpiled
into javascript.

4. Which of the Angular life cycle
component execution happens when
a data-bound input value updates?
ngOnChanges is the life cycle hook that gets
executed whenever a change happens to
the data that was bound to an input.

5. Differentiate between
Components and Directives in
Angular .
Components break up the application
into smaller parts; whereas, Directives
add behavior to an existing DOM
element.

6. What is the use of @Input and
@Output?
When it comes to the communication of Angular
Components, which are in Parent-Child
Relationship; we use @Input in Child Component
and
@Output is used in Child Component to receive
an event from Child to Parent Component.

What does a router.navigate do?
When we want to route to a component we use
router.navigate.
Syntax:
this.router.navigate([‘/component_name’]);

9. What is ViewEncapsulation?
ViewEncapsulation decides whether the styles defined in a
component can affect the entire application or not. There
are three ways to do this in Angular:
Emulated: styles from other HTML spread to the
component.
Native: styles from other HTML do not spread to the
component.
None: styles defined in a component are visible to all
components.

10. What are Services in Angular and
what command is used to create a
service?
Services help us in not repeating the code. With the
creation of services, we can use the same code from
different components. Here is the command to
create a service in angular, ng g service User (a
UserService is created when this command is used).

In how many ways the Data Binding
can be done?
Data Binding happens between the
HTML (template) and typescript
(component). Data binding can be done
in 3 ways:
(i) Property Binding
(ii) Event Binding
(iii) Two-Way Data Binding.

What is the sequence of Angular
Lifecycle Hooks?
OnChange()
- OnInit()
- DoCheck()
- AfterContentInit()
- AfterContentChecked()
- AfterViewInit()
- AfterViewChecked()
- OnDestroy().

What is the purpose of using
package.json in the angular project?
With the existence of package.json, it will be easy
to manage the dependencies of the project. If we
are using typescript in the angular project then we
can mention the typescript package and version of
typescript in package.json.

How is SPA (Single Page Application)
technology different from the
traditional web technology?
In traditional web technology, the client requests
for a web page (HTML/JSP/asp) and the server
sends the resource (or HTML page), and the client
again requests for another page and the server
responds with another resource. The problem
here is a lot of time is consumed in the
requesting/responding or due to a lot of
reloading. Whereas, in the SPA technology, we
maintain only one page (index.HTML) even though
the URL keeps on changing.

What are ngModel and how do we
represent it?
ngModel is a directive which can be applied on
a text field. This a two-way data binding.
ngModel is represented by [()]

Differentiate between Observables
and Promises.
Observables are lazy, which means nothing
happens until a subscription is made. Whereas
Promises are eager; which means as soon as a
promise is created, the execution takes place.
Observable is a stream in which passing of zero or
more events is possible and the callback is called for
each event. Whereas, promise handles a single
event.

What is an AsyncPipe in Angular?
When an observable or promise returns something,
we use a temporary property to hold the content.
Later, we bind the same content to the template.
With the usage of AsyncPipe, the promise or
observable can be directly used in a template and a
temporary property is not required.

Explain Authentication and
Authorization.
Authentication: The user login credentials are passed to an
authenticate API (on the server). On the server side validation
of the credentials happens and a JSON Web Token (JWT) is
returned. JWT is a JSON object that has some information or
attributes about the current user. Once the JWT is given to
the client, the client or the user will be identified with that
JWT.
Authorization: After logging in successfully, the
authenticated or genuine user does not have access to
everything. The user is not authorized to access someone
else’s data, he/she is authorized to access some data.

What is AOT Compilation?
Every angular application gets compiled internally.
The angular compiler takes javascript code,
compiles it and produces javascript code again.
Ahead-of-Time Compilation does not happen every
time or for every user, as is the case with Just-In-
Time (JIT) Compilation.

What is Redux?
It is a library which helps us maintain the state of
the application. Redux is not required in
applications that are simple with the simple data
flow, it is used in Single Page Applications that have
complex data flow.

What are the Pipes?
This feature is used to change the output on the
template; something like changing the string into
uppercase and displaying it on the template. It can
also change Date format accordingly.

Why Typescript with Angular?
Typescript is a superset of Javascript. Earlier, Javascript was
the only client-side language supported by all browsers. But,
the problem with Javascript is, it is not a pure Object
Oriented Programming Language. The code written in JS
without following patterns like Prototype Pattern becomes
messy and finally leading to difficulties in maintainability and
reusability. Instead of learning concepts (like patterns) to
maintain code, programmers prefer to maintain the code in
an OOP approach and is made available with a programming
language like Typescript was thus developed by Microsoft in a
way that it can work as Javascript and also offer what
javascript cannot ;

pure OOPS as Typescript offers concepts like Generics, Interfaces and Types
(a Static Typed Language) which makes it is easier to catch incorrect data
types passing to variables.
TS provides flexibility to programmers experienced in java, .net as it offers
encapsulation through classes and interfaces.
JS version ES5 offers features like Constructor Function, Dynamic Types,
Prototypes. The next version of Javascript ie ES6 introduced a new feature
like Class keyword but not supported by many browsers.
TS offers Arrow Functions (=>) which is an ES6 feature not supported by
many browsers directly but when used in TS, gets compiled into JS ES5 and
runs in any browser.
TS is not the only alternative to JS, we have CoffeeScript, Dart(Google).
Finally, it is like, TS makes life easier when compared to JS.

Angular interview questions

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Angular interview questions