How to call javascript function from Controller

$.ajax({            type: "POST",            url: "/Controller/Action", // the URL of the controller action method            data: null, // optional data            success: function(result) {                 // do something with result            },                            error : function(req, status, error) {                 // do something with error               }        });

Share the code plzz if you want more clear answer.

Abhishek