Angular Interview Question Set 3

Categories: Angular

What are controllers?

AngularJS controllers control the data of AngularJS applications. They are regular JavaScript Objects. The ng-controller directive defines the application controller.


What do you understand by scope in Angular?

The scope in Angular binds the HTML, i.e., the view, and the JavaScript, i.e., the controller. It as expected is an object with the available methods and properties. The scope is available for both the view and the controller. When you make a controller in Angular, you pass the $scope object as an argument. 


 Explain the lifecycle hooks in Angular

In Angular, every component has a lifecycle. Angular creates and renders these components and also destroys them before removing them from the DOM. This is achieved with the help of lifecycle hooks. Here's the list of them - 

  1. ngOnChanges() - Responds when Angular sets/resets data-bound input properties.
  2. ngOnInit() - Initialize the directive/component after Angular first displays the data-bound properties and sets the directive/component's input properties/
  3. ngDoCheck() - Detect and act upon changes that Angular can't or won't detect on its own.
  4. ngAfterContentInit() - Responds after Angular projects external content into the component's view.
  5. ngAfterContentChecked() - Respond after Angular checks the content projected into the component.



 What is String Interpolation in Angular?

String Interpolation is a one-way data-binding technique that outputs the data from TypeScript code to HTML view. It is denoted using double curly braces. This template expression helps display the data from the component to the view. 

{{ data }}



What are Template statements?

Template statements are properties or methods used in HTML for responding to user events. With these template statements, the application that you create or are working on, can have the capability to engage users through actions such as submitting forms and displaying dynamic content.

For example, 

<button (click)="deleteHero()">Delete hero</button>

The template here is deleteHero. The method is called when the user clicks on the button.



What is the difference between AOT and JIT? 

Ahead of Time (AOT) compilation converts your code during the build time before the browser downloads and runs that code. This ensures faster rendering to the browser. To specify AOT compilation, include the --aot option with the ng build or ng serve command. 

The Just-in-Time (JIT) compilation process is a way of compiling computer code to machine code during execution or run time. It is also known as dynamic compilation. JIT compilation is the default when you run the ng build or ng serve CLI commands. 



Explain the @Component Decorator.

TypeScript class is one that is used to create components. This genre of class is then decorated with the "@Component" decorator. The decorato‚Äôs purpose is to accept a metadata object that provides relevant information about the component.  



What are Services in Angular? 

Angular Services perform tasks that are used by multiple components. These tasks could be data and image fetching, network connections, and database management among others. They perform all the operational tasks for the components and avoid rewriting of code. A service can be written once and injected into all the components that use that service. 


What are Promises and Observables in Angular? 

While both the concepts deal with Asynchronous events in Angular, Promises handle one such event at a time while observables handle a sequence of events over some time. 

Promises - They emit a single value at a time. They execute immediately after creation and are not cancellable. They are Push errors to the child promises. 



What is ngOnInit? How is it defined? 

ngOnInit is a lifecycle hook and a callback method that is run by Angular to indicate that a component has been created. It takes no parameters and returns a void type.

export class MyComponent implements OnInit {

constructor() { }

  ngOnInit(): void {

 //....


  }

}

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