Angular2 + Typescript Demo Plunk

<!DOCTYPE html>
<html>

  <head>
    <base href="." />
    <title>angular2 rxjs BehaviorSubject + Subscription</title>
    <script src="https://unpkg.com/zone.js@0.6.21/dist/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="https://unpkg.com/typescript@1.8.10/lib/typescript.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>

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/bundles/core.umd.js',
    '@angular/common': 'npm:@angular/common/bundles/common.umd.js',
    '@angular/compiler': 'npm:@angular/compiler/bundles/compiler.umd.js',
    '@angular/platform-browser': 'npm:@angular/platform-browser/bundles/platform-browser.umd.js',
    '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic.umd.js',
    '@angular/http': 'npm:@angular/http/bundles/http.umd.js',
    '@angular/router': 'npm:@angular/router/bundles/router.umd.js',
    '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js',
    
    '@angular/core/testing': 'npm:@angular/core/bundles/core-testing.umd.js',
    '@angular/common/testing': 'npm:@angular/common/bundles/common-testing.umd.js',
    '@angular/compiler/testing': 'npm:@angular/compiler/bundles/compiler-testing.umd.js',
    '@angular/platform-browser/testing': 'npm:@angular/platform-browser/bundles/platform-browser-testing.umd.js',
    '@angular/platform-browser-dynamic/testing': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic-testing.umd.js',
    '@angular/http/testing': 'npm:@angular/http/bundles/http-testing.umd.js',
    '@angular/router/testing': 'npm:@angular/router/bundles/router-testing.umd.js',
    
    'rxjs': 'npm:rxjs'
  },
  //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 {NgModule, onInit} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import {Component1} from './component1'
import {Component2} from './component2'


@NgModule({
  imports: [ BrowserModule ],
  declarations: [ Component1, Component2 ],
  bootstrap: [ Component1 ]
})
export class AppModule {}

import { Injectable } from '@angular/core'
import { BehaviorSubject } from 'rxjs/BehaviorSubject'

@Injectable()
export class ApiService {
  titleSource = new BehaviorSubject<string>('initial Title')
  titleData$ = this.titleSource.asObservable()
  
  update(newTitle: string){
    console.log('service sent: ' + newTitle)
    this.titleSource.next(newTitle)
  }
}

import { Component } from '@angular/core'
import { ApiService } from './api.service'
import { BehaviorSubject } from 'rxjs/BehaviorSubject'

@Component({
    selector: 'component2',
    providers: [ApiService],
    template: `<button (click)="update()">update root component's title</button>`
})

export class Component2 {
  constructor(private _api: ApiService){}
  
  update(){
    this._api.update('The new updated title which will not be delivered')
  }
}

import {Component, onInit} from '@angular/core'
import {Component2} from './component2'
import {ApiService} from './api.service'
import {Subscription} from 'rxjs/Subscription'


@Component({
  selector: 'my-app',
  directives: [Component2],
  providers: [ApiService],
  template: `
    <div>
    <h3>Root Component</h3>
    Title: {{title}} <br /><br />
    
    <h3>Child Component</h3>
      <component2></component2>
    </div>
  `,
})

export class Component1 implements onInit {
  subscription: Subscription
  title = 'default'
  constructor(private _api: ApiService){}
  
  ngOnInit() {
    this.subscription = this._api.titleData$.subscribe(res => this.title = res)
  }
}