Get Sharepoint site collection id (SPSite.ID) and web id (SPWeb.ID) from followed sites returned from REST API

In Sharepoint we can fetch all followed sites for the current user by the following REST API endpoint:

http://example.com/_api/social.following/my/Followed(types=4)

(instead of http://example.com you should use url of your SP site). It will return collection of site objects which will contain such properties as name, url, etc. However often we need to know also site collection id (SPSite.ID) and web id (SPWeb.ID). We can of course go through all returned sites and fetch their ids by separate JSOM/CSOM calls but it will affect performance (it is classic n+1 problem when we at first get list of items (1st call) and then for each item in the list make separate API call (n calls)).

Fortunately it is possible to get these ids right from REST API response. There is one strange field called "id" which looks like this:

"Id": "8.b4af2aa5fb834daa87aa9fb4155abd7d.b14bd3b3d6084dadb0fc7b79679fc767.
b4af2aa5fb834daa87aa9fb4155abd7d.00000000000000000000000000000000",

So there are several strings divided by dot. If we will check site and web id we will see that second string looks like SPSite.ID and 3rd string like SPWeb.ID:

The only difference is that they don't contain dashes. But it is quite easy do add them by ourselves in the code:

id.substr(0, 8) + "-" + id.substr(8, 4) + "-" + id.substr(12, 4) + "-" + id.substr(16, 4) + "-" + id.substr(20)

Using this approach we can get ids of Sharepoint site collections and web sites directly from REST API response.