CODEWITHSUNDEEP
javascriptangularjsq
TheHippo
TheHippo

Reputation: 63189

Reject a chained promise

The angular docs say you could chain promises, like this:

promiseB = promiseA.then(function(result) {
    return result + 1;
});

Is it possible to reject promiseB from within the function?

promiseB = promiseA.then(function(result) {
    if (result > 0) {
        return result + 1;
    }
    else {
        // reject promiseB
    }
});

P.S.: In this example I assume that promiseA always resolves.

Upvotes: 3

Views: 129

Answers (2)

JoshSGman
JoshSGman

Reputation: 449

You can, in fact, the .then() function takes two callback functions. One for success, and one for an error as specified in that same documentation. In the error handler callback you can use $q.reject() to reject the promise. However, with that said, you can also use it in the success callback too:

  promiseB = promiseA.then(function(result) {
    // success: do something and resolve promiseB
    //          with the old or a new result

    if (!result || result !== "Whatever you're looking for" ) { 
        $q.reject("A Reason")
    } // additional edit from me

    return result;
  }, function(reason) {
    // error: handle the error if possible and
    //        resolve promiseB with newPromiseOrValue,
    //        otherwise forward the rejection to promiseB
    if (canHandle(reason)) {
     // handle the error and recover
     return newPromiseOrValue;
    }
    return $q.reject(reason);
  });

* Taken from Angular Documentation

Upvotes: 2

pkozlowski.opensource
pkozlowski.opensource

Reputation: 117370

promiseB = promiseA.then(function(result) {
    if (result > 0) {
        return result + 1;
    }
    else {
        return $q.reject('whatever reason');
    }
});

This works sine the return value of the success callback of the promiseA gets converted into another promise that is either resolved with the return value of the success callback or rejected if we explicitly reject it with $q.reject or throw an exception.

Upvotes: 3

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