Not understand result from $(window).width()

Question

I have several pages and I notice one strange moment, this code:

var w = $(window).width();
alert(w);

• sometimes returns result: 1440, (and this is true, my screen resolution is 1440 x 900)
• sometimes (in different pages) returns: 1423.

From whence this result, I dont understood.

$(window).width() must be always (from all pages) return the same result, mustn't it?

Answer 1

The scrollbar is not included. From your results, 1440 - 1423 = 17px, which is the same width as my scrollbar (e.g. here on Stack Overflow).

Answer 2

It returns 1423 when you have the scrollbar visible.

The width returned when the scrollbar is visible might change on different browsers and operating systems.