NG Interview Set II - Part 1 Flashcards
NG Interview Set II - Part 1
What is the difference between AngularJS and Angular?
- Angular is a completely revived component-based framework in which an application is a tree of individual components
Some differences are:
AngularJS:
AngularJS:
It is based on MVC architecture
This uses use JavaScript to build the application
Based on controllers concept
Not a mobile friendly framework
Difficulty in SEO friendly application development
Angular:
This is based on Service/Controller
Introduced the typescript to write the application
This is a component based UI approach
Developed considering mobile platform
Ease to create SEO friendly applications
What is TypeScript?
``
TypeScript is a typed superset of JavaScript created by Microsoft that adds optional types, classes, async/await, and many other features, and compiles to plain JavaScript. Angular built entirely in TypeScript and used as a primary language.
You can install it globally as
~~~
npm install -g typescript
~~~
Let’s see a simple example of TypeScript usage,
```typescript
function greeter(person: string) {
return “Hello, “ + person;
}
let user = “Sudheer”;
document.body.innerHTML = greeter(user);
~~~
The greeter method allows only string type as argument.
Write a pictorial diagram of Angular architecture?
What are the key components of Angular?
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 are directives?
- Directives add behaviour to an existing DOM element or an existing component instance
typescript import { Directive, ElementRef, Input } from '@angular/core'; @Directive({ selector: '[myHighlight]' }) export class HighlightDirective { constructor(el: ElementRef) { el.nativeElement.style.backgroundColor = 'yellow'; } }
Now this directive extends HTML element behavior with a yellow background as below
Highlight me!
What are components?
- Components are the most basic UI building block of an Angular app which formed a tree of Angular components
- These components are subset of directives
- Unlike directives, components always have a template and only one component can be instantiated per an element in a template
typescript import { Component } from '@angular/core';
@Component({
selector: 'my-app',
template: {{title}}
Learn Angular6 with examples
``
})
export class AppComponent { title: string = 'Welcome to Angular world'; }
What are the differences between Component and Directive?
- In a short note, A component(@component) is a directive-with-a-template
Some of the major differences are mentioned in a tabular form:
Component
- To register a component we use @Component meta-data annotation
- Components are typically used to create UI widgets
- Component is used to break up the application into smaller components
- Only one component can be present per DOM element
- @View decorator or templateurl/template are mandatory
Directive
- To register directives we use @Directive meta-data annotation
- Directive is used to add behavior to an existing DOM element
- Directive is use to design re-usable components
- Many directives can be used per DOM element
- Directive doesn’t use View
What is a template?
- A template is a HTML view where you can display data by binding controls to properties of an Angular component
- You can store your component’s template in one of two places
- You can define it inline using the template property, or you can define the template in a separate HTML file and link to it in the component metadata using the @Component decorator’s templateUrl property
What is a module?
- Modules are logical boundaries in your application and the application is divided into separate modules to separate the functionality of your application
- Lets take an example of app.module.ts root module declared with @NgModuledecorator as below
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
@NgModule ({ imports: [BrowserModule], declarations: [AppComponent], bootstrap: [AppComponent] }) export class AppModule { }
The NgModule decorator has three options:
- The imports option is used to import other dependent modules. The BrowserModule is required by default for any web based angular application
- The declarations option is used to define components in the respective module
- The bootstrap option tells Angular which Component to bootstrap in the application
What are lifecycle hooks available?
Angular application goes through an entire set of processes or has a lifecycle right from its initiation to the end of the application.
- ngOnChanges: When the value of a data bound property changes, then this method is called.
- ngOnInit: This is called whenever the initialization of the directive/component after Angular first displays the data-bound properties happens.
- ngDoCheck: This is for the detection and to act on changes that Angular can’t or won’t detect on its own.
- ngAfterContentInit: This is called in response after Angular projects external content into the component’s view.
- ngAfterContentChecked: This is called in response after Angular checks the content projected into the component.
- ngAfterViewInit: This is called in response after Angular initializes the component’s views and child views.
- ngAfterViewChecked: This is called in response after Angular checks the component’s views and child views.
- ngOnDestroy: This is the cleanup phase just before Angular destroys the directive/component
What is a data binding?
- Data binding is a core concept in Angular and allows to define communication between a component and the DOM, making it very easy to define interactive applications without worrying about pushing and pulling data
- There are four forms of data binding (divided as 3 categories) which differ in the way the data is flowing
i. From the Component to the DOM: Interpolation: {{ value }}: Adds the value of a property from the component
`
Name: {{ user.name }}
Address: {{ user.address }}
`
Property binding: [property]=”value”: The value is passed from the component to the specified property or simple HTML attribute
`
input type=”email” [value]=”user.email” >`
ii. From the DOM to the Component: Event binding: (event)=”function”: When a specific DOM event happens (eg.: click, change, keyup), call the specified method in the component
< button (click)="logout()" > < /button >
iii. Two-way binding: Two-way data binding: [(ngModel)]=”value”: Two-way data binding allows to have the data flow both ways. For example, in the below code snippet, both the email DOM input and component email property are in sync
< input type=”email” [(ngModel)]=”user.email” >
What is metadata?
- Metadata is used to decorate a class so that it can configure the expected behavior of the class
- The metadata is represented by decorators
i. Class decorators, e.g. @Component and @NgModule
import { NgModule, Component } from '@angular/core';
@Component({
selector: 'my-component',
template:
'< div > Class decorator < /div > ', })
export class MyComponent {
constructor() {
console.log('Hey I am a component!'); } }
@NgModule({
imports: [],
declarations: [],
})
export class MyModule { constructor() { console.log('Hey I am a module!'); } }
ii. Property decorators Used for properties inside classes, e.g. @Input and @Output
import { Component, Input } from ‘@angular/core’; @Component({ selector: ‘my-component’, template: ‘
Property decorator
})
export class MyComponent { @Input() title: string; }
Method decorators Used for methods inside classes, e.g. @HostListener
import { Component, HostListener } from ‘@angular/core’;
@Component({
selector: ‘my-component’,
template: ‘
Method decorator
‘ })
export class MyComponent {
@HostListener(‘click’, [‘$event’])
onHostClick(event: Event) { // clicked, event available } }
iii. Parameter decorators Used for parameters inside class constructors, e.g. @Inject
import { Component, Inject } from ‘@angular/core’; import { MyService } from ‘./my-service’;
@Component({
selector: ‘my-component’,
template: ‘
Parameter decorator
‘ })
export class MyComponent {
constructor(@Inject(MyService) myService) { console.log(myService); // MyService } }
What is angular CLI?
- Angular CLI(**Command Line Interface**) is a command line interface to scaffold and build angular apps using nodejs style (commonJs) modules
- You need to install using below npm command
``
npm install @angular/cli@latest
- Below are the list of few commands, which will come handy while creating angular projects
- Creating New Project: ng new
- Generating Components, Directives & Services: ng generate/g The different types of commands would be, * ng generate class my-new-class: add a class to your application * ng generate component my-new-component: add a component to your application * ng generate directive my-new-directive: add a directive to your application * ng generate enum my-new-enum: add an enum to your application * ng generate module my-new-module: add a module to your application * ng generate pipe my-new-pipe: add a pipe to your application * ng generate service my-new-service: add a service to your application
- Running the Project: ng serve
What is the difference between constructor and ngOnInit?
- TypeScript classes has a default method called constructor which is normally used for the initialization purpose
- Whereas ngOnInit method is specific to Angular, especially used to define Angular bindings
- Even though constructor getting called first, it is preferred to move all of your Angular bindings to ngOnInit method
- In order to use ngOnInit, you need to implement OnInit interface as below:
export class App implements OnInit{
constructor(){
//called first time before the ngOnInit()
} ngOnInit(){
//called after the constructor and called after the first ngOnChanges()
}
}
- the constructor is a default method of the class that is executed when the class is instantiated and ensures proper initialization of fields in the class and its subclasses
- Angular (more precisly the Dependency Injector (DI)) analyzes the constructor parameters and when it creates a new instance by calling new MyClass() it tries to find providers that match the types of the constructor parameters, resolves them and passes them to the constructor
- ngOnInit is a life cycle hook called by Angular2 to indicate that Angular is done creating the component
- mostly we use ngOnInit for all the initialization/declaration and avoid stuff to work in the constructor
- the constructor should only be used to initialize class members but shouldn’t do actual “work”
What is a service?
- is used when a common functionality needs to be provided to various modules
- allows for greater separation of concerns for your application and better modularity by allowing you to extract common functionality out of components
- create a repoService which can be used across components:
import { Injectable } from '@angular/core';
import { Http } from '@angular/http';
@Injectable() // The Injectable decorator is required for dependency injection to work
export class RepoService{
constructor(private http: Http){ }
fetchAll(){
return this.http.get(
'https://api.github.com/repositories').
map(res => res.json());
` }`
}
