Knockout.js - Reload a dropdown with new options using the value of another drop down - mvvm

Question

I've seen similar things, where people have wanted to do this in ASP .NET, generic JavaScript, PHP, etc., but now here we have KnockOut that throws a wrench in things, since its fields are already rendered dynamically. Now here I go wanting to rewrite a dropdown when another is changed... dynamic loading on top of dynamic loading, all in old-fashioned cascading style....
I have a dropdown, "ourTypes", I've called it, that when changed, should re-write the options of the "slots" dropdown to its left. I have a .subscribe() function that creates new options based on a limit I get from the "ourTypes" value. All well and good, but how do we make the dropdown actually reflect those new values?
HTML:
<select data-bind="options: $root.slots, optionsValue: 'Value', optionsText: 'Text', value: $data.SlotPosition"></select>
<select data-bind="options: $root.ourTypes, optionsValue: 'ID', optionsText: 'Name', value: $data.OurTypeId"></select>
JavaScript:
var slots = [
{ Text: "1", Value: "1" },
{ Text: "2", Value: "2" },
{ Text: "3", Value: "3" }
];
var ourTypes = [
{ ID:"1", Name:"None", Limit:0 },
{ ID:"2", Name:"Fruits", Limit:5 },
{ ID:"3", Name:"Vegetables", Limit:5 },
{ ID:"4", Name:"Meats", Limit:2 }
];
var dataList = [
{ SlotPosition: "1", OurTypeId: 4 },
{ SlotPosition: "2", OurTypeId: 2 },
{ SlotPosition: "3", OurTypeId: 3 }
];
var myViewModel = new MyViewModel(dataList);
ko.applyBindings(myViewModel);
function MyViewModel(dataList) {
var self = this;
self.slots = slots;
self.ourTypes = ourTypes;
self.OurTypeId = ko.observable(dataList.OurTypeId);
self.SlotPosition = ko.observable(dataList.SlotPosition);
self.OurTypeId.subscribe(function() {
if (!ko.isObservable(self.SlotPosition))
self.SlotPosition = ko.observable("1");
// Get our new limit based on value
var limit = ko.utils.arrayFirst(ourTypes, function(type) {
return type.ID == self.OurTypeId();
}).Limit;
// Build options here
self.slots.length = 0;
self.slots.push({Text:"",Value:""});
for (var i=1; i < limit+1; i++) {
self.slots.push({Text:i, Value:i});
}
// What else do I do here to make the dropdown refresh
// with the new values?
});
}
Fiddle: http://jsfiddle.net/navyjax2/Lspwc4n4/

Answer 1

Well just made small changes in you code
View Model:
self.slots = ko.observableArray(slots); //should make it observable
self.ourTypes = ko.observableArray(ourTypes);
self.OurTypeId = ko.observable(dataList[0].OurTypeId); // initial value setting
self.SlotPosition = ko.observable(dataList.SlotPosition);
//Inside subscribe
self.slots([]); // clearing before filling new values
Working fiddle here