Question

I’m reading the deferred object in jQuery. Could anyone please tell me what’s the difference between following two invoking way?

1. $.when.apply(null, a method).done(function(){success callback})
2. $.when.(a method).done(function(){success callback})

And what kind of cases are fit for the first way above?

Thanks in advance.

Answer 1

$.when.apply(null, a method) only makes sense if a method is actually an array or a method call returning an array. Then it’s like a $.when(elements, of, the, array). See MDN for a detailed description of the apply method.

$.when.(a method) makes no sense at all, but I guess you meant $.when(a method). In this case a method should again be a method call returning a deferred object or a variable that points to a deferred object.

The syntax of $.when() is $.when(one, or, more, deferreds) – so if you want to pass multiple deferreds which are in an array, you need .apply() since you don’t want to build the method call as a string and use eval (which is indeed evil in this case).