Knockoutjs在与绑定的内部使用foreach传递值时抛出引用错误

我正在尝试使用knockoutjs动态创建选择输入。

我的视图是这样的-

<div data-bind="with: QuestionFilter">
  <form>
    <div>
      <select data-bind="options: categories, optionsText: 'name', optionsValue: 'categoryID', value: selectedCategory">
      </select>
    </div>
    <div data-bind="foreach: details">
      <select data-bind="options: subcategories, optionsText: 'name', optionsValue: 'categoryID', value: selectedSubcategory">
      </select>
    </div>
  </form>
</div>  
<script type="text/javascript">
  ko.applyBindings({
    categories =  <?php echo json_encode($categories); ?>,        
    details = ko.observableArray([])       
  });
</script>

我的JS是这样的-

function QuestionFilter(categories, details) {
  var self = this;
  self.categories = ko.observableArray(categories);
  self.subcategories = ko.observableArray([]);
  self.selectedCategory = ko.observable();
  self.selectedSubcategory = ko.observable();
  self.superSubcategories = ko.observableArray([]);
  self.selectedCategory.subscribe(function(category) {
    function search(nameKey, myArray){
      for (var i=0; i < myArray.length; i++) {
        if (myArray[i].parentCategory_id === nameKey) {
          self.subcategories.push(myArray[i]);
        }
      }
    }   
    search(category, categories);
    details.push({ firstName: self.subcategories()});
  });
  self.selectedSubcategory.subscribe(function(subcategory) {
    function subsearch(nameKey, myArray){
      for (var i=0; i < myArray.length; i++) {
        if (myArray[i].parentCategory_id === nameKey) {
          self.superSubcategories.push(myArray[i]);
    }
      }
    }
   subsearch(subcategory, categories);
   details.push({ firstName: self.superSubcategories()});
  });

因此，变量selectedCategory将按预期执行并触发self.selectedCategory.subscribe中的函数。变量selectedSubcategory不会像预期的那样执行，而是抛出以下错误- ReferenceError: selectedSubcategory is not defined。我认为这与使用with绑定内部的foreach绑定有关，但我不确定。其他一切都像预期的那样工作，我甚至使用它成功地将几个对象添加到details数组中。

有什么想法或需要澄清吗?