The combination of the baseUrlForSite and siteForUrl callbacks configures a site mapping for multi-site support. By configuring a site mapping, you enable Scrivito to differentiate between multiple sites by their individual site IDs and URLs. Scrivito uses this mapping to determine the site the browser is currently displaying, for example. It is also used for cross-site-navigation, i.e. to generate the appropriate URL when a link on the current site points to a page on a different site.

Scrivito always calls your siteForUrl function with an absolute URL, i.e. including host, protocol etc. Similarly, your baseUrlForSite callback is expected to always return an absolute URL as well.

If siteForUrl is invoked with a URL that is not part of your application, your function must return undefined, to indicate to Scrivito, that this is an external URL.

In the example above, the callback returns a valid site ID for "mysite.net/de" and "mysite.net/en", but if invoked with "mysite.net/some_dummy_value" it would probably return undefined to signal to Scrivito that this URL does not denote a valid site. Scrivito treats this as “site not found”, meaning that it is not responsible for rendering this URL, i.e. both Scrivito.currentPage and Scrivito.currentSiteId will return null, and neither Scrivito.CurrentPage nor Scrivito.NotFoundErrorPage will render anything.

Here is a simple example in which Scrivito recognizes only two sites:

Note that sites and URLs can also be mapped dynamically, i.e., without having to change the configuration.

Providing the mapping is optional. If no mapping is given, Scrivito assumes that your CMS is not multi-site, i.e. that it handles just one site. If the mapping is present, however, both functions must be provided (defining just one function is considered an error).