title: When is rxjs observable subscribe executed synchronously?
body: <p>With below code block,</p>
  
  <pre class="lang-js prettyprint-override"><code>let ob = of(1,2,3);
  ob.subscribe((v)=&gt;{
     console.log(v)
  })
  console.log("end")
  </code></pre>
  
  <p>the values are emitted synchronously. Is the function within subscribe guaranteed to be executed before print <code>end</code>?
   so the output will always be.</p>
  
  <pre><code>1
  2
  3
  end
  </code></pre>