title: How to subscribe to array change?
body: <p>I am wondering if it's possible to subscribe to a change object, that is an array. My use case is the following: user reloads a page, that requires the whole collection to be loaded, and then get one object with a specific id. As I know, I can create a function like this:</p>
  
  <p>In constructor:</p>
  
  <pre><code>this.getById(id);
  </code></pre>
  
  <p>And the function</p>
  
  <pre><code>getById(id: string){
      this.object = this.objectsService.getById(id);
      if (this.object.name){ //check if object exist
          //Do something
      } else {
          setTimeout(()=&gt;{
              this.getById(id)
          }, 1000);
      }
  }
  </code></pre>
  
  <p>However, I got a feeling that this is not the best thing to do. So, what I would like to do is something like this:</p>
  
  <pre><code>let objects = this.objectService.getObjects() // returns object that will hold the collection;
  objects.subscribe((value) =&gt; { 
      if(value.length) {
          //Do something
      }
  });
  </code></pre>