title: Angular 2 combine three http calls with flatMap? RxJs?
body: <p>I can find plenty of examples with chaining two calls but i have 3 http calls to make one after another using data from the previous call.</p>
  
  <p>I have two working using flatMap</p>
  
  <p>so:</p>
  
  <pre><code>call1(params)
    .flatMap((res1)=&gt; {
       return call2(params)
          .subscribe(r=&gt;r...)
  </code></pre>
  
  <p>But for three calls i am trying the same thing but i don't think you can chain flatMaps together?</p>
  
  <pre><code>call1(params)
    .flatMap((res1)=&gt; {
       return call2(params)
          .flatMap((res2)=&gt; {
              return call3(params)
                 .subscribe(r=&gt;r...)
  </code></pre>
  
  <p>I get an error saying subscription is not assignable to type observation input. Each of those call1 returns an observable from an http operation.</p>
  
  <p>Can anyone point me in the right direction?</p>
  
  <p>Would really appreciate it as it's driving me nuts!</p>
  
  <p>thanks
  Paul</p>