$.contains returns true if elements are different and lack 'contains' methods

[[email protected]…]

e.g.

elem1 = $('<div></div>'); elem2 = $('<p></p>');

$.contains(elem1, elem2); = true $.contains(elem2, elem1); = true

[sindresorhus]

$.contains ​docs:

Check to see if a DOM element is within another DOM element.

$.contains doesn't support jQuery objects, only vanilla DOM elements.

[dmethvin]

In general a non-chained method like $.method usually accepts a DOM element, not a jQuery object. It's intended as a low-level method.

[[email protected]…]

Should it not return false then or even better throw an error? Why do JavaScript libraries so rarely throw errors? Is this against some kind of policy?

[dmethvin]

The reason that JavaScript APIs don't usually throw errors intentionally is that it is expensive to check all the argument counts and types. Instead, we document the valid inputs and outputs of the API at ​http://api.jquery.com . I don't know what $.contains([{}], {}) or $.contains(new Date, "March", 4) does but those are not valid calls.