I noticed that in 1.4, data() now returns null instead of undefined if nothing has been set for a given key. However, in Firefox 3.6 (Mac and Win), passing an object to console.log() first, then trying to retrieve data for a non-existent key yields undefined (as was the behavior in jQuery 1.3).

Not sure if this is a Firebug problem more than a jQuery problem, but I thought it was worth looking into.

I tried this in Safari and Chrome on Mac and got null before and after the conole.log() call.

Here's some sample code I used to test this:

$(document).ready(function () {

var myElement, myData;

myElement = $("#MyElement");

myData = myElement.data("myKey");

console.log(myData); null

console.log(myElement);

myData = myElement.data("myKey");

console.log(myData); undefined

});