jQuery.contains()

The $.contains() method returns true if the DOM element provided by the second argument is a descendant of the DOM element provided by the first argument, whether it is a direct child or nested more deeply. Otherwise, it returns false. Only element nodes are supported; if the second argument is a text or comment node, $.contains() will return false.

The DOM element that may contain the other element.

The DOM element that may be contained by (a descendant of) the other element.

Check if an element is a descendant of another.

$.contains( document.documentElement, document.body ); // true
$.contains( document.body, document.documentElement ); // false