How to reject a promise from inside then function

Question

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); ?

Answer 1

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     });