Communicator between siblings using interface

<!DOCTYPE html>
<html>

  <head>
    <base href="." />
    <script type="text/javascript" charset="utf-8">
      window.AngularVersionForThisPlunker = '4.3.0'
    </script>
    <title>angular playground</title>
    <link rel="stylesheet" href="style.css" />
    <script src="https://unpkg.com/core-js@2.4.1/client/shim.min.js"></script>
    <script src="https://unpkg.com/zone.js@0.8.12/dist/zone.js"></script>
    <script src="https://unpkg.com/zone.js@0.8.12/dist/long-stack-trace-zone.js"></script>
    <script src="https://unpkg.com/reflect-metadata@0.1.3/Reflect.js"></script>
    <script src="https://unpkg.com/systemjs@0.19.31/dist/system.js"></script>
    <script src="config.js"></script>
    <script>
    System.import('app')
      .catch(console.error.bind(console));
  </script>
  </head>

  <body>
    <my-app>
    loading...
  </my-app>
  </body>

</html>

/* Styles go here */

### Angular Starter Plunker - Typescript

var angularVersion;
if(window.AngularVersionForThisPlunker === 'latest'){
  angularVersion = ''; //picks up latest
}
else {
  angularVersion = '@' + window.AngularVersionForThisPlunker;
}

System.config({
  //use typescript for compilation
  transpiler: 'typescript',
  //typescript compiler options
  typescriptOptions: {
    emitDecoratorMetadata: true
  },
  paths: {
    'npm:': 'https://unpkg.com/'
  },
  //map tells the System loader where to look for things
  map: {
    
    'app': './src',
    '@angular/core': 'npm:@angular/core'+ angularVersion + '/bundles/core.umd.js',
    '@angular/common': 'npm:@angular/common' + angularVersion + '/bundles/common.umd.js',
    '@angular/compiler': 'npm:@angular/compiler' + angularVersion  + '/bundles/compiler.umd.js',
    '@angular/platform-browser': 'npm:@angular/platform-browser' + angularVersion + '/bundles/platform-browser.umd.js',
    '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic' + angularVersion + '/bundles/platform-browser-dynamic.umd.js',
    '@angular/http': 'npm:@angular/http' + angularVersion + '/bundles/http.umd.js',
    '@angular/router': 'npm:@angular/router' + angularVersion +'/bundles/router.umd.js',
    '@angular/forms': 'npm:@angular/forms' + angularVersion + '/bundles/forms.umd.js',
    '@angular/animations': 'npm:@angular/animations' + angularVersion + '/bundles/animations.umd.js',
    '@angular/platform-browser/animations': 'npm:@angular/platform-browser' + angularVersion + '/bundles/platform-browser-animations.umd.js',
    '@angular/animations/browser': 'npm:@angular/animations' + angularVersion + '/bundles/animations-browser.umd.js',
    
    '@angular/core/testing': 'npm:@angular/core' + angularVersion + '/bundles/core-testing.umd.js',
    '@angular/common/testing': 'npm:@angular/common' + angularVersion + '/bundles/common-testing.umd.js',
    '@angular/compiler/testing': 'npm:@angular/compiler' + angularVersion + '/bundles/compiler-testing.umd.js',
    '@angular/platform-browser/testing': 'npm:@angular/platform-browser' + angularVersion + '/bundles/platform-browser-testing.umd.js',
    '@angular/platform-browser-dynamic/testing': 'npm:@angular/platform-browser-dynamic' + angularVersion + '/bundles/platform-browser-dynamic-testing.umd.js',
    '@angular/http/testing': 'npm:@angular/http' + angularVersion + '/bundles/http-testing.umd.js',
    '@angular/router/testing': 'npm:@angular/router' + angularVersion + '/bundles/router-testing.umd.js',
    'tslib': 'npm:tslib@1.6.1',
    'rxjs': 'npm:rxjs@5.4.2',
    'typescript': 'npm:typescript@2.2.1/lib/typescript.js'
  },
  //packages defines our app package
  packages: {
    app: {
      main: './main.ts',
      defaultExtension: 'ts'
    },
    rxjs: {
      defaultExtension: 'js'
    }
  }
});

//main entry point
import {platformBrowserDynamic} from '@angular/platform-browser-dynamic';
import {AppModule} from './app';

platformBrowserDynamic().bootstrapModule(AppModule)

//our root app component
import {Component, NgModule, VERSION} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import {FirstComponent} from './first.component'
import {SecondComponent} from './second.component'
import {Communicator} from './communicator.service'
import {FormsModule} from "@angular/forms"

@Component({
  selector: 'my-app',
  template: `
    <first-component></first-component>
    <br/>
    <second-component></second-component>
    <br/>
  `,
})
export class App {
  name:string;
  constructor() {
    this.name = `Angular! v${VERSION.full}`
  }
}

@NgModule({
  imports: [ BrowserModule, FormsModule ],
  declarations: [ App,FirstComponent, SecondComponent ],
  bootstrap: [ App ],
    providers:[Communicator]
})
export class AppModule {}

import {Component,OnInit} from '@angular/core'
import {Communicator} from './communicator.service'

@Component({
  selector: 'first-component',
  template: '<h1>First Component (Sender)</h1><input type="text" [(ngModel)]="message"/><button (click)="onClick()">Send</button><div>{{status}}</div>'
})
export class FirstComponent implements OnInit {
  message: string;
  status: string;
  
  constructor(private _communicator:Communicator) {
  }
  
  onClick() {
    this.status = this._communicator.receiver.receiveMessage(this.message);
  }
}

import {Component} from '@angular/core'
import {Communicator} from './communicator.service'

@Component({
  selector: 'second-component',
  template: '<h1>Second Component</h1><span>{{message}}</span>'
})
export class SecondComponent implements IReceiver {
  private message: string;
  
  constructor(private _communicator:Communicator) {
    _communicator.receiver = this;
  }

  public receiveMessage(message:string) : string {
    this.message = message;
    return message + " Received";
  }
}

import { Injectable } from '@angular/core';
import {FirstComponent} from './first.component';
import {SecondComponent} from './second.component';
import {IReceiver} from './ireceiver.interface';

@Injectable()
export class Communicator {
  public receiver : IReceiver;
  
}

interface IReceiver {
  receiveMessage: (message:string) => string
};