jQuery返回窗口对象

Question

This is a really stupid question, but for the life of me I can't understand:

Why $(button).addClass('focus') returns DOMNodes

but

(button.addClass || $(button).addClass)('focus') returns the Window object ?

EDIT: Is this linked to JavaScript indirect calls, like : (1, alert)('test') ?

Answer 1

jQuery functions can be chained. This is done by putting return this; at the end of its functions.

However, when you do (button.addClass || $(button).addClass)('focus') , you are dereferencing the function and its context is lost. window is the default context (unless you're in Strict Mode, in which case I think it's null (but as a non-Strict Mode user, I don't know for sure)) which is why you get the Window back.

Also any attempt to chain this function would fail.

Answer 2

What you essentially are doing is this:

var fn;
if (button.addClass)
    fn = button.addClass;
else
    fn = $(button).addClass;
fn('focus');

Hence, you lose the reference to either button or $(button).