just-boris just-boris - 6 months ago 16
AngularJS Question

Angularjs promise rejection chaining

I need to create chained promises:

var deferred = $q.defer();
$timeout(function() {
deferred.reject({result: 'errror'});
}, 3000);
deferred.promise.then(angular.noop, function errorHandler(result) {
//some actions
return result;
}).then(function successCallback(result) {
console.log('what do I do here?');
return result;
}, function errorCallback(result) {
$scope.result= result;
return result;
});


If I put an errorCallback into the first
then
, the second
then
will be resolved and its successCallback will be called . But if I remove
errorHandler
then second promise will be rejected.

According to Angular JS docs the only way to propagate rejection is to return
$q.reject();
and it looks not obvious, especially because I have to inject
$q
service even if it is not needed;

It can also be done by throwing an exception in
errorHandler
, but it writes exception trace to console, it is not good.

Is there another option to do this in a clear way? And what is the reason? Why it is done? In which case, the current behavior can be useful?

ant ant
Answer

And what the reason why it is done. In which case, the current behavior can be useful?

It can be useful when in errorHandler you could try to repair error state and resolve promise somehow.

var retriesCount = 0;

function doWork()
{
    return $http.post('url')
        .then(function(response){
            // check success-property of returned data
            if(response.data.success)
                // just unwrap data from response, may be do some other manipulations
                return response.data;
            else
                // reject with error
                return $q.reject('some error occured');
        })
        .then(/*skip success handler >> */null, function(reason){
            if(retriesCount++ < 3)
                // some error, let me try to recover myself once again
                return doWork();
            else
                // mission failed... finally reject
                return $q.reject(reason);
        });
}


doWork().then(console.log, console.error);
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