For in is meant for iterating over members of an object, $.each is meant to iterate over items of an array, so I'm not sure why the comparison is valid. Sure you can use a for in to iterate over an array, but that's because of the way javascript represents arrays.

I don't think this is something we should really be concerned with. Would you propose a null check and then immediately return if it is null? I think this fits under garbage in garbage out.

@boushley

you want me to post the patch?

each: function( object, callback, args ) {

+ if (object == null) return null;

var name, i = 0,

If the code can't help itself but pass null/undefined then just guard against it with $.each(obj||[],function(){alert(1)}) and all is well. That way we don't mask problems and devs can either explicitly say they don't mind null (as above) or figure out why they are getting it in the first place.

same for underscore.js

http://jsfiddle.net/BW2F2/

works without exceptions:

var each = _.each = _.forEach = function(obj, iterator, context) {
    if (obj == null) return;
...

Replying to [comment:4 theaspect@…]:

i've tested and same behavior in Dojo, ExtJS, Mootools

your antispam system sux

same for underscore.js http://jsfiddle.net/BW2F2/ works without exceptions:

> var each = _.each = _.forEach = function(obj, iterator, context) {
>     if (obj == null) return;
> ...
> 

This is intended and expected behaviour

#9974 is a duplicate of this ticket.

#9989 is a duplicate of this ticket.