determine if a path is relative or absolute

Question

Is there a simple regex to determine if a path is relative, or a hash?

I want to match these:

../index.php  
js/funct.js  
./home/
php/file.php?url=http://www.google.com
index.html#about=http://www.google.com

but not these:

http://www.google.com
http://google.com
/index.php
/
//google.com
#div4

here's what I have so far:

/^[^#\/]|\/\//.test(url)

But it's not working. Is there any way to get this to work?

btw I realize that //google.com is technically relative but I still don't want to match that case

I need this to be able to tell if I need to deal with a link after a pushState. Consider if I started on / and then pushState d to /page1/ then a link that has a href of 'index2.html' was supposed to go to /index2.html but will now go to /page1/index2.html

So I need to check for those types of relative paths.

Answer 1

Don't use low-level stuff like regexp etc. These things have been solved by so many other people. Especially the edge cases.

Have a look at URI.js , it should do the job: http://medialize.github.io/URI.js/docs.html#is

var uri = new URI("/example.org/");
uri.is("relative") === true;

Answer 2

It should not start with a slash or hash, and it should not contain a double slash if not preceded by question mark or hash? I would not test that with a single regexp, it would be very complicated to match "no double slash".

function test(s) {
    return s.charAt(0) != "#"
      && s.charAt(0) != "/"
      && ( s.indexOf("//") == -1 
        || s.indexOf("//") > s.indexOf("#")
        || s.indexOf("//") > s.indexOf("?")
    );
}

would be easier, clearer and imho faster.

Answer 3

Neither of the mentioned solutions solved a redirect_url hack where the hacker entered /\\/example.com or /\\\\/example.com . This is what I came up with to determine if our redirect url was relative:

var isRelative = !redirectUrl.match(/(\:|\/\\*\/)/);  // Don't allow "//" (with optional "\"'s) or ":"