I know how to chain promises so that multiple success functions are executed. That is esplained in many examples. How do I chain promises so that multiple error functions are executed?
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2For me it's not a duplicate. Thanks for answering my question.Galdor– Galdor2015-04-13 14:59:02 +00:00Commented Apr 13, 2015 at 14:59
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2 Answers
When an error is handled (and, either a value is returned or no value at all), the promise returned from then is considered resolved. You have to return a rejected promise from each error handler in order to propagate and chain error handlers.
For example:
promseA.then(
function success() {
},
function error() {
return $q.reject();
})
.promiseB.then(
function success() {
},
function error() {
return $q.reject();
})
.promiseC.then(
function success() {
},
function error() {
return $q.reject();
});
4 Comments
Benjamin Gruenbaum
When a rejected promise has an rejection handler that promise still stays rejected since promises never transition once they resolved. The returned promise from the thenable chaining is resolved if the value returned from the promise error handler is not a rejected promise
Michael Kang
I think we are saying the same thing. When I said "the promise is considered resolved, I was actually referring to the promise returned from the then call. However, my wording could be clearer...
Benjamin Gruenbaum
Thanks for clarifying, found a duplicate but good answer now nontheless.
Max Koretskyi
@pixelbits,
return $q.reject() is indeed a better option than throwing, but maybe you could add this option to your answer as well so that OP if sees this technique will recognize it.then/fail function returns a promise, which can be rejected by throwing errors. If you want to chain multiple error handlers and trigger them all you should throw error from preceding error handlers.
var d = $q.defer();
d.promise.catch(errorHandler1).catch(errorHandler2);
d.reject();
function errorHandler1 {
throw new Error();
}
function errorHandler2() {
console.log("I am triggered");
}
Or instead of catch, you can use then method and pass errorHandler1 and errorHandler2 as a second parameter.
9 Comments
Benjamin Gruenbaum
This will log an error to
$exceptionHandler in Angular, also I don't think this is what OP wants.Max Koretskyi
Right, I didn't know that there is such option
return $q.reject();. It's much better then throwing an error. Is this also standard for Q library and not only angular's $q?Benjamin Gruenbaum
In Q it's perfectly fine to
throw since the $exceptionHandler hack does not exist - although you should really not be using Q in new code anymore.Max Koretskyi
although you should really not be using Q in new code anymore - do you mean in angular code?
Benjamin Gruenbaum
Yes, returning a rejected promise behaving this way is a requirement of the Promises/A+ standard. It will behave consistently across all Promises/A+ implementations.
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