How to set default values for Angular 2 component properties?

In Angular 2, we can pass the value of a variable between two components (from parent to child) using the Input Decorator. Using these Input decorators we can also set the default values of the properties. Below I had detailly elaborated in a comprehensive way on how to set default values for Angular 2 component.

Syntax:

@Input() PropertyName = Default Value  /* @Input country = 'India' */

Approach:

• First code the .html file with respect to requirements.
• Then include the default property in the child component.
• Now initialize the property with a default value using the @Input() decorator.
• We should also import the Input decorator from '@angular/core'.
• Once initialization is completed, use the property in HTML file to display in the browser.

import { Input } from '@angular/core';

Implementation by code: app.component.html:

<p>Welcome to GeeksforGeeks </p>
<app-child [country] = "countryName"></app-child>

app.component.ts:
 

import { Component } from '@angular/core';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ]
})
export class AppComponent  {
  constructor() { }
  ngOnInit() {}
  countryName = 'India';
}

child.component.ts:

import { Component, Input, OnInit} from '@angular/core';

@Component({
  selector: 'app-child',
  templateUrl: './child.component.html'
})
export class ChildComponent implements OnInit {
  constructor() { }
  ngOnInit() {}
  
  @Input() country = 'Australia';
  @Input() capital = 'New Delhi';

}

child.component.html:

<p> Country is : {{country}} </p>
<p> Capital is : {{capital}} </p>

Conclusion:
As we are passing country property as 'India', it will be displayed. But when it comes to capital as we are not passing any value it displays the default value in child.component.ts file.

Output: