Is there any envent when i get focus a dropdownlist?

<pre lang="c#">  ddlsample.Attributes.Add("onmouseover", "OnDDLFocus();");

var ddlCountries;
      function OnDDLFocus() {
          ddlCountries = document.getElementById("<%=ddlsample.ClientID %>");
          ddlCountries.options.length == 0;
          AddOption("Loading", "0");
          PageMethods.getElemnts(OnSuccess);
      }

      function OnSuccess(response) {
          ddlCountries.options.length = 0;
          AddOption("Please select", "0");
          var availableArray = response;
          for (var i = 0; i < availableArray.length; i++) {
              AddOption(i, availableArray[i]);
          }
      }
      function AddOption(value,text) {
          var option = document.createElement("option");
          option.Text = text; option.Value = value;
          ddlCountries.options.add(option);
          option.innerText = text;
      }