问knockout.js为<select>和<option>绑定不同文本

EN

var ItemModel = function(value){
  var self = this;

  self.value = ko.observable(value);
  self.text = ko.computed(function(){
    val = self.value();
    if (val.length > 15){
      return val.substring(0, 15) + "...";
    }
    return val;
  });
};

self.listOptions = ko.observableArray([
    new ItemModel('Neque porro quisquam est qui dolorem ipsum quia dolor sit amet, consectetur, adipisci'),
    new ItemModel('Neque porro quisquam est qui dolorem ipsum'),
    new ItemModel('Proin ultrices, tellus id placerat congue, neque justo commodo purus, et pulvinar massa')
]);

<select data-bind="foreach: listOptions, value: selectedValue, attr: {title : selectedValue}" >
  <option data-bind="text: text, value: value"></option>
</select>