REST API to, given a site URL, get the top level site of that URL (sharepoint 2010, 2013 and 2016)

Question

I've got a sharepoint site with multiple site collections.

/ site collection:

http://mysite/    <--- root site in `/` site collection
http://mysite/subsite1
http://mysite/subsite2

/sitecol1 site collection:

http://mysite/sitecol1/   <-- root site in `/sitecol1` site collection
http://mysite/sitecol1/mysubsiteinsitecol1
http://mysite/sitecol1/mysubsiteinsitecol2

Using rest api, how can I given http://mysite/sitecol1/mysubsiteinsitecol2 determine what root site colleciton it is from?

UPDATE:

Forgot to mention - I need this to work on SharePoint 2010, 2013 and 2016.

Answer 1

You can use REST API to get to the root site. Try this below endpoint in your browser. Append this after your site URL -

/_api/site/rootweb?$select=Title,ServerRelativeUrl,URL

The URL value will give your root site collection

Answer 2

You can make use of the _spPageContextInfo object to get the URL making use of the siteAbsoluteUrl property as:

var siteUrl = _spPageContextInfo.siteAbsoluteUrl

Another way to determine the site collection url is to make a JSOM call :

var clientContext = new SP.ClientContext();
var site = clientContext.get_site();
clientContext.load(site);
clientContext.executeQueryAsync(function(){ 
    console.log(site.get_url()); 
},
function(){
    console.log("something went wrong");
});