Using Slice With Array Created By Knockout's Mapping Plugin

Question

I've been struggling with this all day and I'm not sure what I'm missing. I have a working grid created using Knockout. I'm trying to convert the grid to use the mapping plugin and it breaks my paging. How do I use the slice function with the mapping plugin to return a subset of my array? What am I missing?

var grid = {};
grid.Model = function (jsondata) {
 var viewModel = {
  items: ko.observableArray()
 };

 $.getJSON('/api/test/items', function (data) {
  viewModel.items= ko.mapping.fromJS(data);
  ko.applyBindings(viewModel)
 });

 viewModel.itemsOnCurrentPage = ko.computed(function () {
  return viewModel.items.slice(1, 10);
 }, viewModel);    
};

I'm attempting to bind to itemsOnCurrentPage (foreach: itemsonCurrentPage). Binding directly to items works fine. This worked when I was manually building my array on the client side. Now I'm grabbing the data via jQuery and using the mapping plugin. I can't figure out what I'm missing. Any help would be much appreciated.

Answer 1

RP is correct.

Here is a JSFiddle that shows what you are doing:

http://jsfiddle.net/jearles/P99zy/

Here is an update that works:

http://jsfiddle.net/jearles/P99zy/2/

The only difference is the way I load the table items.

Answer 2

Your issue is that the itemsOnCurrentPage computed observable is bound against your original observableArray. When you do viewModel.items = ko.mapping.fromJS(data), you are setting viewModel.items equal to a new observableArray (one that itemsOnCurrentPage is not bound against).

You can instead do: ko.mapping.fromJS(data, {}, viewModel.items) to update the existing observableArray.