Relative URLs in AJAX requests

Question

Why does Javascript treat relative URLs differently than standard HTML? Think of the following URL (or just browse to it): http://en.wikipedia.org/wiki/Rome. Open a Firebug

Answer 1

Looks like http://code.google.com/p/js-uri/ is the library of choice for URL manipulation in general and this type of absolute-to-relative computation in particular:

new URI(potentiallyRelativeLink).resolve(new URI(window.location.href)).toString()

Answer 2

(updated to make it more readable)

This is how relative paths is supposed to work.

Pretend that the current address is this:

Absolute: protocol://some.domain.name/dir1/dir2/filename

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If you specify only a new filename "foo", you get the same protocol, host and dirs, only the file name is changed:

Relative: foo

Absolute: protocol://some.domain.name/dir1/dir2/foo

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If you specify a whole path "/dir3/filename2" you get the same protocol and hostname but with another path:

Relative: /dir3/filename2

Absolute: protocol://some.domain.name/dir3/filename2

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You can also specify host name "//another.domain.name/dir5/filename3" and get the same protocol but another host, dir and filename:

Relative: //another.domain.name/dir5/filename3

Absolute: protocol://another.domain.name/dir5/filename3

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What might be confusing is that a webserver internally can add a / at the end of the url if the specified url points to a directory and not to a file.

protocol://some.domain.name/somename

If "somename" is a directory the webserver might translate it to (possible with a redirect)

protocol://some.domain.name/somename/

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UPDATE

As cameron said in a comment: For reference, see step 6 in section 4 of RFC 1808