title: Fire and forget in an Observable chain with RxJS
body: <p>Let's say I have 2 functions which return an Observable each</p>
  
  <ul>
  <li><code>getUsersDataObs()</code>: the returned Observable calls an http endpoint to get some data related to the user of the app, this Observable emits when the data is received </li>
  <li><code>sendMailObs</code>: the returned Observable calls a mail server to send an email, this Observable emits when the mail server responds with an acknowledgment</li>
  </ul>
  
  <p>I need the user data to create the mail, so I need to call first <code>getUsersDataObs</code> and then <code>sendMailObs</code>.  At the same time I do not need to know whether <code>sendMailObs</code> has completed or not. I just want to send the mail with a "fire and forget" strategy.</p>
  
  <p>The solution I have crafted so far is this</p>
  
  <pre><code>getUsersDataObs().pipe(
     tap(data =&gt; sendMailObs(data).subscribe())
  )
  .subscribe()
  </code></pre>
  
  <p>While this works, we have a subscription within a subscription, which usually is something that looks not so cool. At the same time, considering that what I want is "fire and forget", maybe a subscription within a subscription is the appropriate thing to do.</p>
  
  <p>Any comment on this would be appreciated</p>