Consuming Default messages from Web API

Hello,  in Microsoft Documentation, they say that the new Web API is almost in full parity with the old SOAP  service endpoint.

But I didnt found any examples , or even if I'am able to call system default messages(like RetrieveDuplicates,assign,WinOpportunitty,etc) from the Web API endpoint(specificly from javascript), anyone have any examples, or know if it is possible ?