Python

import cherrypy

class Root:

    @cherrypy.expose
    @cherrypy.tools.json_out()
    @cherrypy.tools.json_in()
    def my_route(self):

        result = {"operation": "request", "result": "success"}

        input_json = cherrypy.request.json
        value = input_json["my_key"]

        # Responses are serialized to JSON (because of the json_out decorator)
        return result

JavaScript

//assuming that you're using jQuery

var myObject = { "my_key": "my_value" };

$.ajax({
    type: "POST",
    url: "my_route",
    data: JSON.stringify(myObject),
    contentType: 'application/json',
    dataType: 'json',
    error: function() {
        alert("error");
    },
    success: function() {
        alert("success");
    }
});