title: caching promises leads to Unhandled promise rejection in Node.js
body: <p>using nodejs v. 7.5.0 I'm getting 
  UnhandledPromiseRejectionWarning &amp;&amp; DeprecationWarning
  I know its part of new features since node 6.6 but the thing I don't understand is that I'm catching that promises just after caching it into a variable. If I don't cache it no warning is thrown.
  this is the code that throws the error:</p>
  
  <pre><code>    let verifyPromise = verifyToken(id_token);
  
      verifyPromise.catch((err) =&gt; {
          log(err);
      });
  
      let verifyOkPromise = verifyPromise.then((login) =&gt; {
  
          return DB_API.getTokenById(id_token);;
      });
  
      verifyOkPromise.catch((err) =&gt; {
          log('error in finding token: ', err);
      });
  
  
      verifyOkPromise.then((dbRes) =&gt; {
          log('loggin res in finding token: ', dbRes);
      });
  </code></pre>
  
  <p>where verifyToken() is a function that checks google auth token and returns a promise.
  node output is the following:</p>
  
  <pre><code>error in finding token:  { CouchbaseError message: 'The key does not exist on the server', code: 13 }
  (node:10961) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): CouchbaseError: The key does not exist on the server
  (node:10961) DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
  </code></pre>
  
  <p>as you can see the promise error branch is regularly catched as it logs as expected but I still get the warning!!!!</p>
  
  <p>while if I just append the catch like this:</p>
  
  <pre><code> verifyPromise.then((login) =&gt; {
          return DB_API.getTokenById(id_token);;
      }).catch((err) =&gt; {
          log('error in finding token: ', err);
      });
  </code></pre>
  
  <p>NO Warning is given!!!
   I think I'm missing something subtle but I don't understand what could be.
  Some one have any clues?
  thanks in advance</p>