When a jQuery object is passed to the $() function, a clone of the object is created. This new jQuery object references the same DOM elements as the initial one.

Returning an Empty Set

As of jQuery 1.4, calling the jQuery() method with no arguments returns an empty jQuery set (with a .length property of 0). In previous versions of jQuery, this would return a set containing the document node.

Calling the jQuery() method with no arguments returns an empty jQuery set (with a .length property of 0). Similarly, if an argument of null, undefined, an empty array ([]), or an empty string ("") is passed, the set contains no elements.

Working With Plain Objects

At present, the only operations supported on plain JavaScript objects wrapped in jQuery are: .data(),.prop(),.on(), .off(), .trigger() and .triggerHandler(). The use of .data() (or any method requiring .data()) on a plain object will result in a new property on the object called jQuery{randomNumber} (eg. jQuery123456789).