Hi,
Does every web request sent the browsers cookie?
I'm not talking page view, but a request for a image, .js file, etc.
Update If a web page has 50 elements, that is 50 requests. Why would it send the SAME cookie(s) for each request, doesn't it cache or know it already has it?
Yes, as long as the URL requested is within the path defined in the cookie (and all of the other restrictions -- secure, httponly, not expired, etc) hold, then the cookie will be sent for every request.
Yes. Every request sends the cookies that belongs to the same domain.
Like: you have 4 cookies at www.stackoverflow.com. If you make a request to www.stackoverflow.com/images/logo.png it will send the cookies too.
But if you request stackoverflow.com/images/logo.png or images.stackoverflow.com/logo.png, if there are no cookies there, so no cookies will be sent.
You can read more about cookies and images requesting, for example, at this StackOverflow Blog Post.
As others have said, if the cookie's host, path, etc. restrictions are met, it'll be sent, 50 times.
But you also asked why: because cookies are an HTTP feature, and HTTP is stateless. HTTP is designed to work without the server storing any state between requests.
In fact, the server doesn't have a solid way of recognizing which user is sending a given request; there could be a thousand users behind a single web proxy (and thus IP address). If the cookies were not sent every request, the server would have no way to know which user is requesting whatever resource.
Finally, the browser has no clue if the server needs the cookies or not, it just knows the server instructed it to send the cookie for any request to foo.com, so it does so. Sometimes images need them (e.g., dynamically-generated per-user), sometimes not, but the browser can't tell.