Pull request here:

https://github.com/jquery/jquery/pull/238

Addresses http://bugs.jquery.com/ticket/2616 and http://bugs.jquery.com/ticket/4459

Since it was 3 years ago, it didn't seem like it's a huge priority. I wanted to make the addition to handle objects without sacrificing the raw speed of $.map for arrays. Underscore.js already implements this: http://documentcloud.github.com/underscore/#map

Here are some benchmarks: http://jsperf.com/old-map-vs-new-map-with-obj-support/2 The last test ($.new_map_forin_2) is the one that is in this pull request.

Some more tests here: http://jsfiddle.net/mmhwZ/16/