convert uri from href/src attribute to absolute-absolute URI given the relative servername and attribute value

uri_to_absolute.js

function uri_to_absolute(server_name, uri) {
  if (uri.match(/^#/)) {
    return uri;
  }
  
  var m = server_name.match(/^((.+?\/\/[^\/]+)(.*))/);

  var server_name = (m) ? m[2] : server_name;
  var path = (m) ? m[3] : '';
  
  // remove trailing slash on server_name if it exists
  if (server_name.match(/\/$/)) {
    m = server_name.match(/^(.+?)\/*$/);
    server_name = m[1];
  }
  
  if (path.length > 0 && !path.match(/\/$/)) { // if the path does not end with a /
    // trim the last path element
    m = path.match(/^(.+?)\/[^\/]+$/);
    path = m[1];
  }
  
  // remove leading slash on path
  if (path.match(/^\//)) {
    m = path.match(/^\/(.*)$/);
    path = m[1];
  }
  
  if (path.length > 0) {
     path = path + '/';
  }
  
  var final_output;
  
  if (uri.match(/^\//)) {               // if the URI starts with a /, then just prepend the server_name
    final_output = server_name + uri; 
  } else if (uri.match(/^.+?:\/\//)) {  // the URI has a protocol defined (http://), so return the uri
    final_output = uri;
  } else {                              // the URI is relative, so 
    final_output = server_name + '/' + path + uri;
  }
  
  // replace double-slashes
  if (final_output.match(/:\/\/.*\/\//)) {
    final_output.replace(/([^:])\/\//, "\1/");
  }
  
  return final_output;
}