And one heck of an inconsistency, don't you think?
jQuery.each() and jQuery.map() don't pass the arguments to their callbacks
in the same order?! That's definitely a mistake.
Actually, the original order chosen for the arguments to the $(...).each()
and $.each() callbacks was unfortunate. callback(index,element) is
backwards. It's rare that you need the array index; what you want in almost
every situation is the array *element*.
The (new) native JavaScript [].forEach() and [].map() methods got it right:
their callbacks receive the arguments in this order:
callback(element,index,array).
The reason we ended up with callback(index,element) was simply that the
original jQuery code didn't have either of those arguments. It was simply
callback() with no arguments, and the array element in "this". The index
argument got added later, and the element argument was added after that. The
order of arguments is simply a historical accident: it's the chronological
order in which the arguments were added to the code!
Why does it matter? Consider the following array:
var array = [
[ 'a', 'b' ],
[ 'c', 'd' ]
];
Now iterate over its elements (in both dimensions) using .forEach() and
$.each():
array.forEach( function( outer ) {
outer.forEach( function( inner ) {
console.log( inner );
});
});
$.each( array, function( i, outer ) {
$.each( outer, function( j, inner ) {
console.log( inner );
});
});
The $.each() version requires placeholder "i" and "j" arguments which the
.forEach() version does not require.
It's a small thing, but if you want to (wisely!) write jQuery quote that
uses explicit callback arguments instead of overusing "this", you have to
throw in those extra arguments every time.
Moot point now, though, it's a done deal.
And given that it's a done deal, $.map() should have been consistent with
the other jQuery callbacks.
Oops... :-)
-Mike
> From: Ariel Flesler
>
> You have both jQuery.fn.map
> http://docs.jquery.com/Traversing/map
>
> And jQuery.map
> http://docs.jquery.com/Utilities/jQuery.map
>
> Both documented correctly.
> On Aug 19, 5:51 pm, moester <[EMAIL PROTECTED]> wrote:
> > The argument order of the $.map callback function seems to be
> > reversed depending on how $.map is used.
> >
> > >>> arr = ['a','b','c']
> >
> > ["a", "b", "c"]
> >
> > >>> $.map(arr,function(n,i){return [n,i]})
> >
> > ["a", 0, "b", 1, "c", 2] <--
> > according to docs
> >
> > >>> $(arr).map(function(n,i){return [n,i]}).get()
> >
> > [0, "a", 1, "b", 2, "c"] <--
> > reverse of docs!!
> >
> > I realize in the second case one could use 'this' to get
> > the value and just use one argument for the index,
> > which is more consistent with other chainable functions.
> > Perhaps this could be made clear in the docs or with an
> > example.
