Change Optionset Values on change of other optionset values using JavaScript in Microsoft Dynamics CRM 2011 and 2013

function optionSetChanged() // apply this function of change of country field
{

    // on the base of country change cities

    var _collection = getCollection();
    var _selectedCity = null;
    var _cityOptionset = Xrm.Page.ui.controls.get("city");  
if (_cityOptionset != null)
    _selectedCity = _cityOptionset.getAttribute().getValue();
var _cityOptions = _cityOptionset.getAttribute().getOptions();
    var _selectedCountry = Xrm.Page.getAttribute("Country").getText();    
    // If Country is empty, then clear the City field.
    if (_selectedCountry == "")
{
        _cityOptionset.clearOptions();
    }
    else
{
        for (var i = 0; i < _collection.length; i++)
{          
if (_selectedCountry.toLowerCase() == _collection[i].Country.toLowerCase())
{                _
cityOptionset.clearOptions();
            for (var j = 0; j < _collection[i].Cities.length; j++)
{                  
for (var k = 0; k < _cityOptions.length; k++)
{                      
if (_collection[i].Cities[j].toLowerCase() == _cityOptions[k].text.toLowerCase())
{                          
_cityOptionset.addOption(_cityOptions[k]);
                        break;
                        }
                    }
                }
                break;
            }
        }    
if (_cityOptionset != null && _selectedCity != null)
            _cityOptionset.getAttribute().setValue(_selectedCity);
    }
}


function getCollection() {

    var _collection = new Array();  
var India_Cities = new Array("NewYork");
    var India_obj = { Country: "USA", Cities: India_Cities };
    _collection.push(India_obj);

    var Srilanka_Cities = new Array("Lahore");
    var SriLanka_obj = { Country: "pakistan", Cities: Srilanka_Cities };
    _collection.push(SriLanka_obj);

    var USA_Cities = new Array("Mumbai");
    var USA_obj = { Country: "India", Cities: USA_Cities };
    _collection.push(USA_obj);

    return _collection;
}