Why "$().ready(handler)" is not recommended?

I got an official answer from one of the jQuery developers:

$().ready(fn) only works because $() used to be a shortcut to $(document) _{(jQuery <1.4)}
So $().ready(fn) was a readable code.

But people used to do things like $().mouseover() and all sorts of other madness.
and people had to do $([]) to get an empty jQuery object

So in 1.4 we changed it so $() gives an empty jQuery and we just made $().ready(fn) work so as not to break a lot of code

$().ready(fn) is literally now just patched in core to make it work properly for the legacy case.

The best place for the ready function is $.ready(fn), but it's a really old design decision and that is what we have now.

I asked him:

Do you think that $(fn) is more readable than $().ready(fn) ?!

His answer was:

I always do $(document).ready(fn) in actual apps and typically there's only one doc ready block in the app it's not exactly like a maintenance thing.

I think $(fn) is pretty unreadable too, it's just A Thing That You Have To Know Works™...

Since the different options do pretty much the same thing as you point out, it's time to put on the library writer hat and make some guesses.

1. Perhaps the jQuery people would like to have $() available for future use (doubtful since $().ready is documented to work, even if not recommended; it would also pollute the semantics of $ if special-cased).

2. A much more practical reason: the second version is the only one that does not end up wrapping document, so it's easier to break when maintaining the code. Example:

   // BEFORE
   $(document).ready(foo);
   
   // AFTER: works
   $(document).ready(foo).on("click", "a", function() {});
   

   Contrast this with

   // BEFORE
   $().ready(foo);
   
   // AFTER: breaks
   $().ready(foo).on("click", "a", function() {});
   

3. Related to the above: ready is a freak in the sense that it's (the only?) method that will work the same no matter what the jQuery object wraps (even if it does not wrap anything as is the case here). This is a major difference from the semantics of other jQuery methods, so specifically relying on this is rightly discouraged.

   Update: As Esailija's comment points out, from an engineering perspective ready should really be a static method exactly because it works like this.

Update #2: Digging at the source, it seems that at some point in the 1.4 branch $() was changed to match $([]), while in 1.3 it behaved like $(document). This change would reinforce the above justifications.

I would say its simply the fact that $() returns an empty object whereas $(document) does not so your applying ready() to different things; it still works, but I would say its not intuitive.

$(document).ready(function(){}).prop("title") // the title
$().ready(function(){}).prop("title")  //null - no backing document