Are 127.0.0.1 and localhost treated as two different domains by browsers?

Question

Are 127.0.0.1 and localhost considered as two different domains by browsers and therefore apply cross-domain restrictions (same initial rules)?

I noticed that it once works (in the case of simple web pages) and does not work with Flex based web pages.

For example: Scenario I: On a webpage named page1.htm, you call the script as follows:

<script type="text/javascript" src="js/somejsscript.js"></script> 

or

 <script type="text/javascript" src="http://localhost/js/somejsscript.js"></script> 

and you access the page as http: //localhost/page1.htm

Scenario II: You invoke the script as follows:

 <script type="text/javascript" src="http://127.0.0.1/js/somejsscript.js"></script> 

and you access the page as http: //localhost/page1.htm

Answer 1

Origin is defined as a scheme / host / port (the port is the default value for the scheme if it does not exist, for example, port 80 for http, 443 for https). The same origin is defined as a matching scheme / host / port. "localhost" and "127.0.0.1" are different hosts in this case. See http://en.wikipedia.org/wiki/Same_origin_policy#Origin_determination_rules

Answer 2

Yes, these are different reasons for securing the Internet; no browsers equate them. Technically, "localhost" can point anywhere, and usually (on modern systems) it points to IPv6, not IPv4.