JS production of simple three-level and joint

Front desk:

<form id="Form1"runat="Server"> <div>Province<SelectId="Province"> <option> Please select </option> </Select>City<SelectId=" City"> <option> Please select </option> </Select>Area<SelectId="Space"> <option> Please select </option> </Select> <script type="Text/javascript">$ (function () {$.ajax ({URL:"testclass/cascade.ashx?id=1",                       Async:false, Success:function (data) {$ ("#Province"). append (data); $("#Province"). Change (function () {$.ajax ({URL:"testclass/cascade.ashx?id=2", data: {pid: $ ("#Province"). attr ("value")}, Success:function (data) {$ ("#City"). HTML (""); $("#City"). append (data); $("#City"). Change (function () {$.ajax ({URL:"testclass/cascade.ashx?id=3", data: {cid: $ ("#City"). attr ("value")}, Success:function (data) { $("#Space"). HTML (""); $("#Space"). append (data);                                   }                                               })                                           })               }                               })                           })                       }                   }) })            </script> </div> </form>

Background:

   Public voidProcessRequest (HttpContext context) {context. Response.ContentType="Text/plain"; if(Context. request.querystring["ID"] =="1")            {                stringsql ="SELECT Id,[enname] from [Provinceinfo] WHERE parentid=0"; StringBuilder SB=NewStringBuilder (); SqlDataReader Reader= Pubsqlhelperfunc.executesqldatareader (CommandType.Text, SQL,NULL);  while(reader. Read ()) {sb. Append ("<option value="); Sb. Append (reader["Id"]); Sb. Append (">"); Sb. Append (reader["Enname"]); Sb. Append ("</option>"); } reader.                Close (); Context. Response.Write (sb.)            ToString ()); }            Else if(Context. request.querystring["ID"] =="2")            {                stringsql ="SELECT Id,[enname] from [Provinceinfo] WHERE parentid="+ context. request.params["PID"] +""; StringBuilder SB=NewStringBuilder (); Sb. Append ("<option> Please select </option>"); SqlDataReader Reader= Pubsqlhelperfunc.executesqldatareader (CommandType.Text, SQL,NULL);  while(reader. Read ()) {sb. Append ("<option value="); Sb. Append (reader["Id"]); Sb. Append (">"); Sb. Append (reader["Enname"]); Sb. Append ("</option>"); } reader.                Close (); Context. Response.Write (sb.)            ToString ()); }            Else if(Context. request.querystring["ID"] =="3")            {                stringsql ="SELECT Id,[enname] from [Provinceinfo] WHERE parentid="+ context. request.params["CID"] +""; StringBuilder SB=NewStringBuilder (); Sb. Append ("<option> Please select </option>"); SqlDataReader Reader= Pubsqlhelperfunc.executesqldatareader (CommandType.Text, SQL,NULL);  while(reader. Read ()) {sb. Append ("<option value="); Sb. Append (reader["Id"]); Sb. Append (">"); Sb. Append (reader["Enname"]); Sb. Append ("</option>"); } reader.                Close (); Context. Response.Write (sb.)            ToString ()); }        }

JS production of simple three-level and joint