andler, even though there is code
  // (just below) to eventually handle the error.
  future.then((value) { useValue(value); },
              onError: (e) { handleError(e); });
});
</code></pre>
<p>When registering callbacks, it's often more readable to register the two
callbacks separately, by first using <a href="dart-async/Future/then.html">then</a> with one argument
(the value handler) and using a second <a href="dart-async/Future/catchError.html">catchError</a> for handling errors.
Each of these will f