dialog: cancel errors with "Possibly unhandled rejection" when no catch exists

[bjarketrux]

Actual Behavior:

• What is the issue? * When calling $mdDialog.show() and the user press cancel, a message is shown in the console: "Possibly unhandled rejection: undefined"
• What is the expected behavior?
  Recently Angular has started to log possibly unhandled rejections commit
  This is a discussion of how to handle the console errors.

1. Give a reason in the reject (Possibly unhandled rejection: User pressed cancel)
2. Do not use reject as a way of dismissing the dialog. According to MDN rejected promises are "almost" the same as throwing an error. This implies that a user clicking cancel is "almost" the same as handling them by throwing an exception.
3. Add a global unhandled rejection event handler to silence all errors (including actual errors):

app.config(['$qProvider', function ($qProvider) {
$qProvider.errorOnUnhandledRejections(false);
}]);

4. Add a catch block to the promise

$mdDialog.show({...})
    .then(confirmUserAction)
    .catch(() => {}); // or angular.noop

What are your thoughts?
Thanks

CodePen (or steps to reproduce the issue): *

• Details:
  Create a dialog with the $mdDialog.show(). Then press the cancel button on the dialog.

Angular Versions: *

• Angular Version: 1.6.1
• Angular Material Version: 1.1.1

Additional Information:

• Browser Type: * Chrome
• Browser Version: * 55
• OS: * MacOS
• Stack Traces:

[nathansherburn]

I think ultimately Solution 2 will be the best way to handle this. I'll be using Solution 4 until we have an answer from the Angular Material team as to weather or not they want to do something like Solution 2. Thanks for posting this by the way!

[keatonboyle]

I agree that Solution 2 is probably the best way to handle this long term. Another option in the interim is something between 3 and 4-- monkey-patch the show() method in a run block rather than changing the global $qProvider or modifying every single use of $mdDialog.show().

Like:

app.run(['$mdDialog', ($mdDialog) => {
  let original = $mdDialog.show;
  $mdDialog.show = (...args) => original(...args).catch(() => {}); // or angular.noop
}]);

I haven't tested this fully. Obviously not ideal.

[trevorhreed]

@keatonboyle I like your thinking. However, this causes the then(...) to always run, which, if cancel is pressed, isn't always a good idea. I've made the following modification, which throws a specific type of error. I've overridden $exceptionHandler to deal with this specific type of error:

module.run(function($mdDialog, $q){
  let original = $mdDialog.show;
  $mdDialog.show = (...args) => {
    return original(...args).catch(() => { throw 'ignore' });
  }
});

module.config(function($provide, HttpError){
  $provide.decorator('$exceptionHandler', function($delegate, $injector){
    return function(exception, cause){
      if(exception === 'Possibly unhandled rejection: ignore') return;
      $delegate(exception, cause);
    }
  });
});

[fsmeier]

+1

[Splaktar]

This is related to #11181.

We have no plans to implement any major changes like Solution 2 would require.
Solution 4 is the recommended approach (along with possibly doing something useful in the catch block).

For reference on Solution 3, you can find the docs for $qProvider.errorOnUnhandledRejections here.

[fsmeier]

In addition to solution 3, dont use noop or any complete hiding solution:

$mdDialog.show({...})
    .then(confirmUserAction)
    .catch(function (err) {
        if (err) {
             console.error(err);
        }
    }); 

[Splaktar]

I believe that the confusion here has been settled and the approaches above are sufficient.