Quick IE compatible method to dynamically filter selections

MapSelections.js

$.fn.showOption = function() {
    this.each(function() {
        var span = $(this).parent();
        var opt = $(this).show();
        $(span).replaceWith(opt)
    });
}
$.fn.hideOption = function() {
    this.each(function() {
        if ($(this).parent()[0].tagName != "SPAN") {
            $(this).wrap('<span>').hide();
        }
    });
}

function filterSelect(parentName, childName)
{
  $("#"+ parentName).change(execFilter);
  execFilter();
  function execFilter()
  {
    var parentValues = $("#" + parentName).val();
    if(parentValues === undefined){
      return;
    }
    
    var childField = $("#" + childName);
    var optionValueSelector;
    if(parentValues.map)
    {
      optionValueSelector = parentValues.map(function(selectedValue)
      {
        return "[value^='" + selectedValue + "-']";
      }).join(",");
    }
    else
    {
      optionValueSelector = "[value^='" + parentValues + "-']";
    }
    var childVal = childField.val();
    childField.find("option").hideOption();
    childField.find("option[value='']," + optionValueSelector).showOption();
    childField.val(childVal);
    childField.val(childField.val());
  }
}