If you are using a function that may return a promise, but just might return a value if it doesn’t need to defer, you can use the “static” methods of the Q library.
The when function is the static equivalent for then.
return Q.when(valueOrPromise, function (value) {
}, function (error) {
});
All of the other methods on a promise have static analogs with the same name.
The following are equivalent:
return Q.all([a, b]);
return Q.fcall(function () {
return [a, b];
})
.all();
When working with promises provided by other libraries, you should
convert it to a Q promise. Not all promise libraries make the same
guarantees as Q and certainly don’t provide all of the same methods.
Most libraries only provide a partially functional then method.
This thankfully is all we need to turn them into vibrant Q promises.
return Q($.ajax(...))
.then(function () {
});
If there is any chance that the promise you receive is not a Q promise
as provided by your library, you should wrap it using a Q function.
You can even use Q.invoke as a shorthand.
return Q.invoke($, 'ajax', ...)
.then(function () {
});