Angular 2: Component Interaction, optional input parameters

You can use the ( ? ) operator as below

import {Component,Input} from '@angular/core';
@Component({
    selector:'child',
    template:`<h1>Hi Children!</h1>
          <span *ngIf="showName">Alex!</span>`
})


export class ChildComponent {

    @Input() showName?: boolean;

    constructor() { }

}

The parent component that uses the child component will be as

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2>Hello {{name}}</h2>
      <child [showName]="true"></child>
      <child ></child>
    </div>
  `,
})
export class App {
  name:string;
  constructor() {
    this.name="Angular2"
  }
}

LIVE DEMO