ko

ko.js

<select data-bind='value:selected, options:availableOptions, optionsText:'name' />
<div data-bind='template:{"name":resolveTemplate, data:selected}' />

var vm = {
  'selected' : ko.observable(''),
  'availableOptions' : ko.ObservableArray([{'name':'foo', 'value':'fooval}, {'name':'bar', 'value':'barval'}]),
  'resolveTemplate' : function(){
     var selectedItem;
     selectedItem = selected();
     if(selectedItem){
         return doSomeLogicOnSelectedItemAndReturnString(selectedItem);
     }
   }
};

//selected will actually hold the observable object of the selected option. So, selected() return {name, value} pair.