Do you need to use jQuery.when with one pending object?

Question

Say you have the following code snippet:

function someProcess() { var deferred = $.Deferred(); apiCall(function (recvData) { deferred.resolveWith(null, [recvData]); }); return deferred.promise(); } function mainFunction() { $.when(someProcess()) .then(someOtherProcess); } 

In this example, I only need to wait until one pending request is resolved. In this case, what is the difference (if any) between writing the second function, as described above, and writing it as follows:

 function mainFunction() { someProcess() .then(someOtherProcess); } 

I mean, I like to write it the first way, because it makes it clear that we are using jQuery pending objects, but I'm curious if this is necessary in this case.

edit: I set a typo in the then () call. Thanks for catching this.

edit: Thanks for the answer nrabinowitz. I think you attached points that I was not sure about when () compared to using a jQuery deferred instance. I went and corrected my code again to return a promise instead of the whole pending object. This is how I do it in my actual code right now, just forgot to add it here.

Answer 1

I did not use deferred custom objects, but I understand that there are two differences in your examples:

• Using $.when() allows you to optionally add additional pending objects for processing by handlers. Obviously, this is not very important, as you will have to modify this line of code to add additional deferrals.

• $.when() receives a Promise object, not the whole pending object, which, if I understand correctly, is a measure of consistency to hide pending state changes (for example, resolve() ), only exposing handler hooks and state control methods. This seems like good practice, but in your example you can do the same by calling someProcess().promise() instead of $.when(someProcess()) .

So, I think you are right - both methods will work, but the main advantage of using $.when() is to make the code more understandable and to correctly determine the expectations for other programmers. Using $.when() or deferred.promise() will additionally help protect against incorrect encoder involvement with the state of your deferred.