How to pass data from Client side to Server side in widget using c.server.update()

We can use c.server.update() method to execute server side script again where it can access client side 'data' object as 'input' object.
Example : Send change number from client side to server side code and get associated assignment group.
Client Script Code :

function() {
/* widget controller */
var c = this;
c.data.chgNumber = "CHG00232";
c.data.actionName="getChangeAssignmentGroup"
c.server.update().then(function(response){
console.log(response.assignment_group;
});
}

Server side code :

if (input) {
if (input.actionName == "getChangeAssignmentGroup") {
var grChange=new GlideRecord("change_request");
if(grChange.get("number",input.chgNumber){
input.assignment_group=grChange.assignment_group;
}
}
}