Ajax Example in coldfusion

<script type="text/javascript">
    function showvalues(str)
    {
        var xmlhttp;   
        if (window.XMLHttpRequest)
          {// code for IE7+, Firefox, Chrome, Opera, Safari
              xmlhttp=new XMLHttpRequest();
          }
        else
         {// code for IE6, IE5
              xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
           }
        xmlhttp.onreadystatechange=function()
          {
          if (xmlhttp.readyState==4 && xmlhttp.status==200)
                {
                    document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
                }
        }
        xmlhttp.open("GET","?city_name="+str,true);
        xmlhttp.send();
    }
</script>

<cfparam name="url.city_name" default="">
<div id="txtHint">City info will be listed here...
    <cfform>
        <cfselect id="city_name" name="city_name" size="1" required="yes" message="Please Select  city_name" onchange="showvalues(this.value);" width="120">
              <option value="" selected="selected">Please select </option>
              <option <cfif url.city_name eq 'City1'>selected="selected"</cfif> value="City1">City1</option>
              <option <cfif url.city_name eq 'City2'>selected="selected"</cfif>value="City2">City2</option>
              <option <cfif url.city_name eq 'City3'>selected="selected"</cfif>value="City3">City3</option>
        </cfselect>
        <cfif isdefined('city_name')     and city_name eq 'City1'>                                                                                                                        
            <cfselect id="sub_city_name" name="sub_city_name" size="1" required="yes" message="Please Select  Sub city_name" width="120">
              <option value="City11">City11</option>
              <option value="City12">City12</option>
              <option value="City13">City13</option>
            </cfselect>
        </cfif>
        <cfif isdefined('city_name')     and city_name eq 'City2'>  
            <cfselect id="sub_city_name" name="sub_city_name" size="1" required="yes" message="Please Select  Sub city_name" width="120">
                  <option value="City21">City21</option>
                  <option value="City22">City22</option>
                  <option value="City23">City23</option>
             </cfselect>
        </cfif>
        <cfif isdefined('city_name')     and city_name eq 'City3'>  
            <cfselect id="sub_city_name" name="sub_city_name" size="1" required="yes" message="Please Select  Sub city_name" width="120">
                  <option value="City31">City31</option>
                  <option value="City32">City32</option>
                  <option value="City32">City32</option>
                 
            </cfselect>
        </cfif>
    </cfform>
</div>