Question

In this commit there is a change I cannot explain

deferred.done.apply( deferred, arguments ).fail.apply( deferred, arguments );

becomes

deferred.done( arguments ).fail( arguments );

AFAIK, when you invoke a function as a member of some object like obj.func(), inside the function this is bound to obj, so there would be no use invoking a function through apply() just to bound this to obj. Instead, according to the comments, this was required because of some preceding $.Callbacks.add implementation.

My doubt is not about jQuery, but about the Javascript language itself: when you invoke a function like obj.func(), how can it be that inside func() the this keyword is not bound to obj?

Answer 1

My doubt is not about jQuery, but about the Javascript language
itself: when you invoke a function like obj.func(), how can it be that
inside func() the this keyword is not bound to obj?

Well, the only way this is possible is if obj.func references a bound function, then it doesn’t matter how you call it. In that case it doesn’t matter how you call the function, whether you do obj.func(), func(), func.call({}), func.apply({}) doesn’t matter at all. I’m not sure how the commit is related to this, however.

To clarify, I am answering the quoted question interpreted as:

Given a call signature like: obj.func(), how is it possible that this is not obj inside the called function for the call?