Hi :)

Here: http://jsfiddle.net/Mr21/wh5sdgzu/
We have a code who execute the .animate methode on a div#A and with the argument progress I can move the div#B in the same way.

I have access to the easing function with this:
$.easing[ anim.opts.easing ]( progress );
but, if I don't set explicitly: easing: "swing" when I call animate it doesn't work.

In the PR #2218, I set a default value jQuery.easing._default = "swing"; to keep consistent with the jQuery.fx.speeds._default = 400;.