Promises and generic .catch() statements

Question

I\'m writing an API for my system, that\'s sending an XHR to the server and returns a promise that should be handled by the caller - so far so good.

For each API cal

Answer 1

I think all you want to do is rethrow the exception after you've logged it so other handlers will deal with it properly:

return deferred.promise.catch(function (error) {
  console.error(error);
  throw e; // rethrow the promise
});

Answer 2

Q use NodeJS process to raise unhandledRejection. If you dont use NodeJS, you can use this Workaround:

// Simulating NodeJS process.emit to handle Q exceptions globally
process = {
    emit: function (event, reason, promise) {
        switch(event)
        {
            case 'unhandledRejection':
                console.error("EXCEPTION-Q> %s", reason.stack || reason)
                break;
        }
    }
}

Answer 3

With bluebird Promises, you can call

Promise.onPossiblyUnhandledRejection(function(error){
    // Handle error here
    console.error(error);
});

With iojs you have the process.on('unhandledRejection') handler as specified here. (Also worth reading this and this

As far as I know, neither native Promises anywhere else nor Q Promises offer this functionality.