What makes $ .if for one $ .Deferred?

Question

I am trying to understand $.when , and I see that this can be useful when you want to wait a few pending until the beginning. However, I'm not sure I understand what is used to use $.when with one pending. To illustrate:

 var deferred = $.Deferred(); // Is this ever useful? $.when(deferred).then(...) // Or can I always do this? deferred.then(...) 

Answer 1

From the $.when ^[docs] documentation:

If one Deferred is passed for jQuery.when , its method returns a Promise object (a subset of the Deferred methods).

So $.when(deferred).then(...) same as deferred.promise().then(...) .

A promise object is a limited interface to a deferred object. It allows you to add callbacks, but not change the status of deferred (allow, reject).

So finally there is no fundamental difference between using $.when and calling .then directly on the deferred object.

I don't think it makes sense to pass one pending object explicitly to $.when , since you are not getting any advantage. However, there may be situations where you have an unknown number of pending objects, which means that it can also be only one.

Answer 2

You can always do .then , .then is nothing more than a shortcut when you need to use both .done and .fail