Question

188

How to reject a promise from inside then function

rated 0 times [ 192] [ 4] / answers: 1 / hits: 56966 / 11 Years ago, tue, january 21, 2014, 12:00:00

This is probably a silly question, but mid promise chain, how do you reject a promise from inside one of the then functions? For example:

someActionThatReturnsAPromise()

    .then(function(resource) {

        return modifyResource(resource)

    })

    .then(function(modifiedResource) {

        if (!isValid(modifiedResource)) {

            var validationError = getValidationError(modifiedResource);

            // fail promise with validationError

        }

    })

    .catch(function() {

        // oh noes

    });

There's no longer a reference to the original resolve/reject function or the PromiseResolver. Am I just supposed to add return Promise.reject(validationError); ?

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milor

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answered 11 Years ago janettejordynm · Accepted Answer

Am I just supposed to add return Promise.reject(validationError);?

Yes. However, it's that complicated only in jQuery, with a Promise/A+-compliant library you also could simply

throw validationError;

So your code would then look like

someActionThatReturnsAPromise()

    .then(modifyResource)

    .then(function(modifiedResource) {

        if (!isValid(modifiedResource))

            throw getValidationError(modifiedResource);

        // else !

        return modifiedResource;

    })

    .catch(function() {

        // oh noes

    });