Angular Promises and Chaining: How to break a chain if it has business data errors

Question

I thought that I had this all figured out on previous projects through the years.. Apparently not.

Goal : Take Service that calls other Services and if there is any

Answer 1

it seems that the promise returned by SparkRequestService.submitRequest(request) is not rejected when you get the error inside resData. For this reason the successCallback of then is invoked and not the second one, the errorCallback.

For this reason, inside the successCallback you need to inspect the data of resData to check errors and behave accordingly, for example:

var getSubmit = function (request) {
    return SparkRequestService
        .submitRequest(request)
        .then(function (resData) {
                console.log("resData", resData);
                if(resData === null) { // Check for errors
                    // There is an error, manage it inside this block of code
                    // ...
                    // You can also create a rejected promise with $q.reject() and passing resData containing the errors
                    return $q.reject(resData);
                } else {
                    // Call resetEnrollment() in the ELSE branch so, it is executed only if resData does not contain errors
                    enrollmentService.resetEnrollment();
                    return resData;
                }
            }, 
            function (resData) {
                console.log('error');
            }
        );
};

Answer 2

To prevent a rejection handler from converting a rejected promise to a fulfilled promise it is important use a throw statement in the rejection handler:

var getSubmit = function (request) {
    return SparkRequestService
        .submitRequest(request)
        .then(
            function (resData) {
                console.log("resData", resData);
                enrollmentService.resetEnrollment();
                return resData;
            }, 
            function (errorResponse) {
                console.log('error');
                //IMPORTANT
                //throw to chain rejection
                throw errorResponse;
            }
        );
}

When a function omits a return or throw statement, the function returns a value of undefined. This will convert a rejected promise to a fulfilled promise that resolves with a value of undefined.

---

Problem is that ... it is a business error wrapped up in a return object

To convert a fulfilled promise to a rejected promise, use a throw statement.

this.submitEnrollment = function (enrollment) {
    var promise = getSubmit(requestData);
    var newPromise = promise.then(function(response) {
         if (response.data.hasErrors) {
             console.log(response.data.errorList);
             response.data.errorList.push("submitEnrollent: Rejected"); 
             //THROW to create rejection
             throw response;
         } else {
             //RETURN response to chain success
             return response;
         }
    });
    return newPromise;
}

When a promise is converted to a rejection, all subsequent success handlers in the chain will be skipped. The chain will be followed until a rejection handler is found.