Possibly unhandled rejection in Angular 1.6

Question

I have a code with AngularJS:

service.doSomething()
  .then(function(result) {
      //do something with the result
  });

In AngularJS 1.5.9 when I have error in the .then() section like:

service.doSomething()
  .then(function(result) {
      var x = null;
      var y = x.y;
      //do something with the result
  });

I'm getting clear error message:

TypeError: Cannot read property 'y' of null

But in version 1.6 with the same code I'm getting a different error:

Possibly unhandled rejection: {} undefined

I know that this is related to this change, and the single solution is quite simple by adding .catch() block:

service.doSomething()
  .then(function(result) {
      var x = null;
      var y = x.y;
      //do something with the result
  })
  .catch(console.error);

Now I again have what I want:

TypeError: Cannot read property 'y' of null

But how to obtain the same result (more detailed error) for entire application without adding .catch() block in every single place?

I tested the suggested solution to disable this by adding:

$qProvider.errorOnUnhandledRejections(false);

But with this the situation is even worse - I do not have ANYTHING in the console! The error is swallowed somewhere and not logged at all. I'm not sure is it a problem with AngularJS 1.6 or with my configuration.

Do you have any ideas how to "restore" logging behavior from version 1.5.9?

EDIT:

Adding custom error handler:

.factory('$exceptionHandler', function($log) {
  return function(exception, cause) {
    $log.warn(exception, cause);
  };
})

does not help at all. In the error handler I already receive the "wrapped" error.

Answer 1

This has been fixed with fix($q): Add traceback to unhandled promise rejections -- Commit 316f60f and the fix is included in the v1.6.1 release.

Answer 2

First option simply is to hide this specific rejection error by setting errorOnUnhandledRejections in $qProvider configuration as suggested Cengkuru Michael:

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

BUT this will only switch off logging. The error itself will remain

The better solution in this case will be - handling a rejection with .catch() method:

service.doSomething()
    .then(function (response) {})
    .catch(function (err) {});

Useful Links:

• Promise
• Migrating Angular 1.5 to 1.6
• $http: remove deprecated callback methods: 'success()/error()'

Answer 3

I fixed the same problem with version 1.6.1 by upgrading angular-ui-router to 0.3.2.

Answer 4

This information helped me to track down what (in my case) was creating the promise and not adding an error handler. I found it buried in the discussion of issue #2889 "Possibly unhandled rejection with Angular 1.5.9".

The gist, is, patch $q to cache a stack-trace on creating promises, such that it can be retrieved when the error is triggered.

To do it, insert this code to decorate $q somewhere near the top of your angular app:

// Decorate the $q service when app starts
app.decorator('$q', ["$delegate", function($delegate) {
  // Create a new promise object
  var promise = $delegate.when();

  // Access the `Promise` prototype (nonstandard, but works in Chrome)
  var proto = promise.__proto__;

  // Define a setter for `$$state` that creates a stacktrace 
  // (string) and assigns it as a property of the internal `$$state` object.
  Object.defineProperty(proto, '$$state', {
    enumerable: true,
    set: function(val) {
      val.stack = new Error().stack;
      this._$$state = val;
    },
    get: function() {
      return this._$$state;
    }
  });

  return $delegate;
}]);

Then search the angular code for the message "possibly unhandled rejection" and put a breakpoint on that line. When the breakpoint is reached, print out the value of toCheck.stack on the console, and you'll see something like this:

>> toCheck.stack
"set@http://localhost:8000/js/dual-site.js:18:19
Promise@http://localhost:8000/js/angular.js:17008:22
then@http://localhost:8000/js/angular.js:17016:20
catch@http://localhost:8000/js/angular.js:17026:14
SyncStrategy.prototype.send@http://localhost:8000/js/angular-state-machine.js:436:24
StateMachine/this.send@http://localhost:8000/js/angular-state-machine.js:235:16

The offending code is the frame calling angular's catch/then functions.