I'm testing jQuery 1.3 beta 1.

In jQuery 1.2.6, it was possible to store empty strings (

""

) and

null

as values for jQuery.data(). If the value was not set or unset, jQuery.data() would return

undefined

.

''Example:''

var value, el = $("#hello")[0];
value = jQuery.data(el, "test");
// value === undefined

jQuery.data(el, "test", "");
value = jQuery.data(el, "test");
// value === ""

jQuery.data(el, "test", null);
value = jQuery.data(el, "test");
// value === null

jQuery.removeData(el, "test");
value = jQuery.data(el, "test");
// value === undefined

However, in jQuery 1.3 beta 1, storing an empty string (

""

) makes jQuery.data() return

null

. Furthermore, if the value was not defined, it also returns

null

instead of

undefined

, so it is not possible to know if a

null

value was actually stored or if no value was stored at all, which makes it practically impossible to store

null

as value as well.

''Same example, different values with 1.3b1:''

var value, el = $("#hello")[0];
value = jQuery.data(el, "test");
// value === null

jQuery.data(el, "test", "");
value = jQuery.data(el, "test");
// value === null

jQuery.data(el, "test", null);
value = jQuery.data(el, "test");
// value === null

jQuery.removeData(el, "test");
value = jQuery.data(el, "test");
// value === null

This means that code which stores empty string values will break because it will get a

null

back instead of a string, and code which relied on the return value being different than

undefined

to confirm that it was set will also break.