title: angular 2 Property 'push' does not exist on type 'Observable'
body: <p>I am having a problem with push data </p>
  
  <p>component.ts </p>
  
  <pre><code>import { Component, OnInit } from '@angular/core';
  
  
  import { AngularFireDatabase } from 'angularfire2/database';
  import { Observable } from 'rxjs';
  
  @Component({
    selector: 'app-content',
    templateUrl: './content.component.html',
    styleUrls: ['./content.component.css']
  })
  
  export class ContentComponent implements OnInit {
  
    courses$:Observable&lt;any[]&gt;;
  
    authors$:Observable&lt;any[]&gt;;
  
    constructor(db:AngularFireDatabase){
      this.courses$ = db.list('/courses').valueChanges();
      this.authors$ = db.object('/authors/1').valueChanges();
  
    }
    add(course:HTMLInputElement){
      this.courses$.push(course.value);
      course.value = '';
    }
  
    ngOnInit() {
  
    }
  
  }
  </code></pre>
  
  <p>html 
  i put input to get the put the input </p>
  
  <pre><code>&lt;input type="text" (keyup.enter)="add()"&gt;
  &lt;ul&gt;
    &lt;li *ngFor="let item of courses$ | async"&gt;
      {{ item | json }}
    &lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>ERROR </p>
  
  <p>content.component.ts (25,19): Property 'push' does not exist on type 'Observable'.</p>