capturing ko.mapping.fromjs changes

[chris green]

Hi Guys,

I've been playing with knockout for a short time and could use some assistance. 

My goal is to develop an application that displays a grid of data, stock prices. These will be updated periodically from the server using Ajax.

So far I have a viewmodel that is created using ko.mapping.fromJS, this is then updating with fresh stock prices from the server using another call to ko.mapping.fromJS. All works well and my view is updated successfully. However what I want to do is capture the change on a per cell basis so that I can update the cell with green for an increase in a cell value or red for a decrease and so far I can't find a way to intercept the event - I'm toying with using expandos on the html but i've seen some negative comments on expandos and can't help but feel there must be a better way. Any ideas?

Thank you for your time.

[Gunnar Liljas]

I would suggest that you don't use ko.mapping at all. It tends to complicate things.

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[chris green]

I see. Is there something in particular you would recommend?

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[Gunnar Liljas]

I would recommend mapping "manually" into StockPrice entities.

var StockPrice=function(val){

    var self=this;
    this.color=ko.observable('white');
    var _val=ko.observable(val);
    this.value=ko.computed({
       write: function(newValue){
           if (_val()==newValue)
           {
              self.color('white');
              return;
           }
           if (_val()<newValue){
              self.color('red');
           } else {
              self.color('green');
           }
       },
       read: function(){
         return _val();
       }

    }
  );

}

[chris green]

Thank you kindly. I'm going make the changes you suggest.