Aura Server Action

// Calling a server-side action
({
    callServerSideAction : function(cmp) {
        // 1. Retrieve an action object by specifying the
        //    Apex method that will be called
        let action = cmp.get("c.myApexEndpoint");

        // 2. Optionally set some action parameters
        action.setParams({ firstName : cmp.get("v.firstName") });

        // 3. Configure a callback function that will be
        //    executed to handle the server response
        action.setCallback(this, function(response) {
            // Some response processing code
            var state = response.getState();
            if (state === "SUCCESS") {
                // Alert the user with the value returned 
                // from the server
                alert("From server: " + response.getReturnValue());

                // You would typically fire a event here to trigger 
                // client-side notification that the server-side 
                // action is complete
            }
            else if (state === "INCOMPLETE") {
                // do something
            }
            else if (state === "ERROR") {
                var errors = response.getError();
                if (errors) {
                    if (errors[0] && errors[0].message) {
                        console.log("Error message: " + 
                                 errors[0].message);
                    }
                } else {
                    console.log("Unknown error");
                }
            }
        });

        // 4. Optionally set some action configuration flags

        // 5. Enqueue the action so that the framework processes it
        $A.enqueueAction(action);
    }
})