how api works

[morplug]

I have been interested in APIs in the last time and i want to know exactly how it works from the server side.

 

so i tried to figure out how the client side API working ,

first step i took the Google Plus One JS client side code and i tried to figure out how it works , mostly i tried to find how it gets connect to the server side.

i couldn't find what this whole code doing , mainly because i focused to find Ajax requests , but there is none of them.

 

this is the api I checked :

 

https://apis.google.com/js/plusone.js

 

now , my questions is simple ,

i want to know how API connect to the server side , do they use AJAX?

what exactly they use to send request to server side ?

 

 

i need you're help to know more on how api working on Client side , mainly on the connect to the server.

so , how it get's done?