How To Call Server Side Method from Javascript by passing Value and Bind data to Drodownlist

Hi Sir,
I want to get Locations  by cityId.I wrote service in code behind like below
[System.Web.Script.Services.ScriptMethod()] [System.Web.Services.WebMethod]
public static List<Location> GetLocation(int cityId)
{
return objcityController.GetCityLocationItem(cityId); }
Now I want to call this Method  from javascript by passing CityId and bind Locations to Drodownlist
Can Any one give me solution.How to do this