I am not sure if this is a bug, a lack of documentation, or a misunderstanding on my part so I apologize in advance.

When using jQuery.extend() to merge 2 objects (obj1, and obj2) into a new empty object (target), any arrays from obj2 are actually shared between instances of target. So if any instance of target modifies the array, all instances see the change.

A code example is worth a thousand words so please check the following jsfiddle: http://jsfiddle.net/WxpSj/1/

I would expect the console output for the array to say just ["cat"] but instead it says ["chicken", "bird", "cat"].