jquery ajax implements three-level no-refresh linkage of the drop-down box, and saves and maintains the selected value_jquery

//获取cookie值
function readCookie(name) {
    var cookieValue = "";
    var search = name + "=";
    if (document.cookie.length > 0) {
        offset = document.cookie.indexOf(search);
        if (offset != -1) {
            offset += search.length;
            end = document.cookie.indexOf(";", offset);
            if (end == -1) end = document.cookie.length;
            cookieValue = unescape(document.cookie.substring(offset, end))
        }
    }

    return cookieValue;
}

//保存cookie值
function writeCookie(name, value, hours, escp) {
    var expire = "";
    if (hours != null) {
        expire = new Date((new Date()).getTime() + hours * 3600000);
        expire = "; expires=" + expire.toGMTString();
    }
    if (escp == "True") {
        document.cookie = name + "=" + value + expire;
    } else {
        document.cookie = name + "=" + escape(value) + expire;
    }
}

//省市区，流域，水系，断面条件选择
$(function() {

    var $ddlprovince = $("#ddlProvince");     //省份
    var $ddlcity = $("#ddlCity");      //城市
    var $ddlarea = $("#ddlAreaName");         //区域

    //根据省份查询城市
    //$ddlprovince.focus(); //不要加focus,否则设置selected有问题
    $ddlprovince.bind("change keyup", function() {
        if ($(this).val() != "-1") {
            loadWater($(this).val(), "SelectCity");
        } else {
            $("select[id$=ddlCity] > option").remove();
            $ddlcity.append($("").val("-1").html("--请选择--"));
        }
        //从新选择省份或者从新选择城市都会初始化区域
        $("select[id$=ddlAreaName] > option").remove();
        $ddlarea.append($("").val("-1").html("--请选择--"));
    });

    //如果城市没有填充数据，省份有选择数据则加载数据
    if ($("select[id$=ddlCity] > option").length == 1 && $ddlprovince.val() != "-1") {

        loadWater($ddlprovince.val(), "SelectCity");
        //读cookie,有值则设为选中状态
        var cityname = readCookie("JQ_CityName");
        if (cityname != null && cityname != "undefined" && cityname != "") {

            //$("select[id=ddlWaterXiName] > option:contains('" + watername + "')").attr("selected", "true");
            $("select[id$=ddlCity] > option[value='" + cityname + "']").attr("selected", "true");
        }
    }

//Query area based on city
//$ddlcity.focus();
$ddlcity.bind("change keyup", function() {
if ($(this).val( ) != "-1") {
                                                                                                                         .val(), 0.5, true);
       } else {
                $("select[name$=ddlAreaName] > option").remove(); ").val("-1").html("--Please select--"));
                                  

//If the district name has no data filled in and the city has selected data, load the data
if ($("select[id$=ddlAreaName] > option").length == 1 && $ddlcity .val ()! = "-1") {
Loadwater ($ ddlcity.val (), "selectareaname"); readCookie("JQ_AreaName");

if (areaname != null && areaname != "undefined" && areaname != "") {

$("select[id=ddlAreaName] > option[ value='" areaname "']").attr("selected", "true");

}
}

$ddlarea.bind("change keyup", function() {
if ($(this).val() != "-1") {
//Select the value to save the cookie

writeCookie("JQ_AreaName", $(this).val(), 0.5, true);

}

});

});

function loadWater(selectedItem, typename) {
$.ajax({
type: "GET",

url: "/GetWaterxiname.ashx",

data: { usetype: typename, id: selectedItem },
contentType: "application/json; charset=utf-8",

dataType: "json",

async: false,
success: function Success(data) {
bindWater(data, typename);
}
});
}

function bindWater(data, typename) {

if (typename == "SelectCity") { //Bind city

                                                                                                                                                                                                                                                                           "").val("-1").html("--Please select--"));

for (var i = 0; i < data.length; i ) {

$("select[id$=ddlCity]").append($("< /option>").val(data[i].City).html(data[i].City));

                                                                                                                           🎜>

$ ("select [name $ = ddlareaname] & gt; option"). Remove (); // Delete the original option

$ ("select [ID $ = ddlareaname]"). "").val("-1").html("--Please select--"));

for (var i = 0; i < data.length; i ) {
$("select[id$=ddlAreaName]").append($("< /option>").val(data[i].AreaName).html(data[i].AreaName));
                                                                                                                                         Province data is bound when the page is loaded. After the page is submitted, the province value can be obtained with selectvalue. The selected data of city and district must be obtained with Request["idname"]