jQuery $().data gotcha: A collection can be removed from and re-added to the DOM, but its data disappears.

jquery-data-removal.js

// Using jQuery 1.3.2:

// Setup:
var $foo = $('<div id="foo"></div>').appendTo('body');
$foo;                   // => [div#foo]
$foo.data('bar', 123);
$foo.data('bar');       // => 123

// Teardown:
$foo.remove();          // => [div#foo]
$foo.data('bar');       // => undefined

// Re-setup:
$foo.appendTo('body');  // => [div#foo]
$foo.data('bar');       // undefined