How to get DataTextField of DropDownList in javascript?

<asp:DropDownList
  ID="ddlLocationName"
  runat="server"
  DataValueField="Guid"
  DataTextField="LocationName"
  AppendDataBoundItems="false"
  AutoPostBack="false"
  onchange="LocationChange()"
></asp:DropDownList>

function LocationChange()
{
  document.getElementById ("ctl00_mainContent_ctl02_txtEventLocation").value = document.getElementById ('ctl00_mainContent_ctl02_ddlLocationName')[document.getElementById ('ctl00_mainContent_ctl02_ddlLocationName').selectedIndex].value
}

function LocationChange(){
  var ddl = $get('dropDownListId');
  var selectedOption = ddl.options[ddl.selectedIndex];
  var selectedText = selectedOption.text;
  var selectedValue = selectedOption.value;

  alert('Your option has a text property of ' + selectedText + ' and a value property of ' + selectedValue');
}

function LocationChange()
{
    document.getElementById ("ctl00_mainContent_ctl02_txtEventLocation").value = document.getElementById ('ctl00_mainContent_ctl02_ddlLocationName')[document.getElementById ('ctl00_mainContent_ctl02_ddlLocationName').selectedIndex].innerText
}