q.js automatically propagate errors (catch async thrown errors)? - q

Question

i would like to know if there's any way to automatically propagate errors from a promise to another? IE: catch the thrown error from a nested promise.
for example, in the following code sample, the "internalWorker" nested promise function needs
.fail(function (error) {
return deferred.reject(error);
});
in order to propagate the error. if this line isn't contained, the error is throw to the top. (crashed app)
would it be possible to automatically propagate the error so i don't need to add .fail() functions to all my nested promises?
```
function top(input) {
var deferred = q.defer();
internalWorker(input).then(function (value) {
logger.inspectDebug("top success", value);
}).fail(function (error) {
return deferred.reject(error);
});
return deferred.promise;
}
function internalWorker(input) {
var deferred = q.defer();
q.delay(100).then(function () {
throw new Error("internal worker async error");
}).fail(function (error) {
return deferred.reject(error);
});
return deferred.promise;
}
top("hello").then(function (value) {
logger.inspectDebug("outside success", value);
}).fail(function (error) {
logger.inspectDebug("outside fail", error);
}).done();
```

Answer 1

If you are using https://github.com/kriskowal/q, this will do what you intend:
function top(input) {
return internalWorker(input).then(function (value) {
logger.inspectDebug("top success", value);
return value;
});
}
function internalWorker(input) {
return q.delay(100).then(function () {
throw new Error("internal worker async error");
return value;
});
}
top("hello").then(function (value) {
logger.inspectDebug("outside success", value);
}, function (error) {
logger.inspectDebug("outside fail", error);
}).done();
Return promises or values from within callbacks. Errors propagate implicitly.