Angular

Question 1

What is Single Page Web Application?

Answer 1

An SPA (Single-page application) is a web app implementation that loads only a single web document, and then updates the body content of that single document via JavaScript APIs

This therefore allows users to use websites without loading whole new pages from the server

Question 2

What are the basic building blocks of Angular Framework?

Answer 2

Angular Components . These are organized into NgModules.

Question 3

What is NgModule in Angular?

Answer 3

An NgModule is a class marked by the @NgModule decorator with a metadata object that describes how that particular part of the application fits together with the other parts.

NgModules collect related code into functional sets;

Question 4

How do components work in angular ?

Answer 4

Components define views, which are sets of screen elements that Angular can choose among and modify according to your program logic and data
Components use services, which provide specific functionality not directly related to views. Service providers can be injected into components as dependencies, making your code modular, reusable, and efficient.

Question 5

What are decorators in Angular ?

Answer 5

Modules, components, and services are classes that use decorators.
These decorators mark their type and provide metadata that tells Angular how to use them.

The metadata for a component class associates it with a template that defines a view.

The metadata for a service class provides the information Angular needs to make it available to components through dependency injection (DI)

Question 6

Why Organizing the code into distinct functional modules is necessary?

Answer 6

Organizing your code into distinct functional modules helps in managing development of complex applications, and in designing for reusability.

In addition, this technique lets you take advantage of lazy-loading —that is, loading modules on demand— to minimize the amount of code that needs to be loaded at startup.

Question 7

Can Modules be loaded asynchronously?

Answer 7

Modules can be loaded eagerly when the application starts or lazy loaded asynchronously by the router.

Question 8

What is a Feature Module?

Answer 8

A feature module collaborates with the root module and with other modules through the services it provides and the components, directives, and pipes that it shares.

Question 9

What is the declarations array in NgModule used for?

Answer 9

The declarations array is available for you to add declarables, which are components, directives, and pipes that belong exclusively to this particular module.

Question 10

What is a Javascript module?

Answer 10

A JavaScript module is an individual file with JavaScript code, usually containing a class or a library of functions for a specific purpose within your application. JavaScript modules let you spread your work across multiple files.

You can Import or Export modules using ‘import’ or ‘export’ keyword.

Question 11

What is root module?

Answer 11

An application always has at least a root module (App Module)that enables bootstrapping and typically has many more feature modules.

Question 12

What are declarations in NgModule?

Answer 12

declarations: The components, directives, and pipes that belong to the NgModule. A new application project’s root NgModule has only one component, called AppComponent.

Question 13

What are imports in NgModule?

Answer 13

imports: Other NgModules you are using, so that you can use their declarables. The newly generated root NgModule imports BrowserModule in order to use browser-specific services such as DOM rendering, sanitization, and location.

Question 14

What are providers in NgModule?

Answer 14

providers: Providers of services that components in other NgModules can use. There are no providers in a newly generated root NgModule.

Question 15

What is bootstrap in NgModule?

Answer 15

bootstrap: The component that Angular creates and inserts into the index.html host web page, thereby bootstrapping the application. This component, AppComponent, appears in both the declarations and the bootstrap arrays.

Question 16

What are directives in Angular?

Answer 16

Structural , Attribute and Components

Question 17

Can we create Custom Structural and Custom Attribute directives ?

Answer 17

We can create custom attribute directive like highlighting the selected element by setting the background color and custom structural directive like notIf which works exact opposite of ngIf

Question 18

What is BrowserModule in Angular?

Answer 18

Should be imported to run your application in a browser.

Question 19

What is CommonModule in Angular?

Answer 19

Should be used if ‘ngIf’ , ‘ngFor’ are used

Question 20

What is FormsModule in Angular ?

Answer 20

To build template driven forms (includes NgModel).

Question 21

What is ReactiveFormsModule in Angular

Answer 21

To build reactive forms.

Question 22

What is RouterModule in Angular?

Answer 22

To use RouterLink, .forRoot(), and .forChild().

Question 23

What is HttpClientModule in Angular?

Answer 23

To communicate with a server using the HTTP protocol.

Question 24

Will Express accept CORS -cross origin requests (Request from other domain) ?

Answer 24

No , By default express doesn’t allow CORS. By using middleware CORS it is possible .

Question 25

What is a stream?

Answer 25

A stream is a sequence of values in time

Question 26

Are streams and observables same?

Answer 26

No

Question 27

What is an Operator in Rxjs?

Answer 27

An operator is a function that takes an Observable, and returns another Observable.

Question 28

What is Functional Reactive programming?

Answer 28

Functional Reactive Programming (FRP) is a paradigm for software development that says that entire programs can be built uniquely around the notion of streams. Not only frontend programs, but any program in general.

Question 29

Does programs built in Functional Reactive programming have state?

Answer 29

the application does have a state, but that state it’s typically stored on certain streams or in the DOM, not on the application code itself.

Question 30

What does cold observable mean?

Answer 30

observable is said to be cold because it does not generate new values if no subscriptions exist.

Question 31

Are observables shared between subscribers?

Answer 31

No, each subscriber gets their own seperate processing chain

Question 32

How does Angular use Observables?

Answer 32

1. As an internal implementation mechanism, to implement some of its core logic like EventEmitter
2. As part of its public API, namely in Forms and the HTTP module

Question 33

What does Map Operator do?

Answer 33

The map operator simply takes an Observable and adds a transforming function that processes the output of the stream.
For Example,
const obs = interval(500)
.pipe(
take(5),
map(i => 2 * i )
);

Question 34

What does Scan Operator do?

Answer 34

To know what is the state of the observable after each element is reduced and react to that instead of only to the final result of the reduction operation.

Question 35

What does Share Operator do?

Answer 35

The share operator allows us to share a single subscription of a processing chain with other subscribers.

Question 36

What does Concat Operator do?

Answer 36

The concat operator combines multiple observables and do consecutive HTTP requests

Question 37

What does retry operator do?

Answer 37

It sends the request(does retry) until it receives the response from the URL

Question 38

What does retryWhen do?

Answer 38

It sends the request(does retry) until it receives the response from the URL based on the condition that is specified inside it.

Question 39

Can we use Event Emitters inside of a router outlet?

Answer 39

<router-outlet> does not offer a means to bind data to loaded components or emit events from them to parents.
</router-outlet>

Question 40

What is Async pipe?